Hundred Summers projects every year of your financial life using UK tax and pension rules and the assumptions below - all published here in full, because you cannot interpret a projection you cannot interrogate. This page is generated from the same code that runs the app.
How this tool works
Transparency about our methodology, assumptions and limitations. Understanding these helps you interpret your projections correctly.
Default assumptions
Every plan-level assumption, its default, and what it drives. Inside the app all of these are editable per plan (Methodology → Plan Assumptions), and your own entries always take precedence.
General inflation (CPI proxy) — 2.5%
Grows living expenses, indexed contributions and every today's-money entry from year 0.
Care cost inflation — 4%
Later-life care costs index at this rate - historically above general inflation.
State Pension growth — 2.5%
Triple-lock proxy; indexes the resolved State Pension from today.
Tax band indexation — 2.5%
Applied to income tax and NI thresholds after the freeze ends (5 April 2031).
Property growth — 2.5%
Applies to every property in the plan.
DB pension indexation — 2.5%
Deferred revaluation before payment and increases in payment.
Equity release interest rate — 6.5%
Compounds the lifetime-mortgage balance when equity release is used.
State Pension deferral uplift — 5.8%
Permanent increase per full year the State Pension is deferred.
Annuity rate override — not set (market table)
When unset, the built-in market-average annuity rate table is used instead.
Pension annual allowance — £60,000
Tapered for high adjusted income; contributions above it get no relief in the model.
ISA allowance — £20,000
Per tax year; enforced on contributions and surplus sweeps, overflow goes to a GIA.
IHT nil-rate band — £325,000
Frozen until April 2030.
IHT residence nil-rate band — £175,000
Requires a home left to direct descendants; tapers above a 2m pound estate.
Ongoing investment charges — 0%
Platform, fund and any adviser fee, deducted from the growth of every invested holding (pensions and non-cash accounts). Individual pots and accounts can override it with their own rate — the per-asset table below shows which. 0% models a portfolio with no costs at all.
Stress-test simulations — 500
Market paths per Monte Carlo run. The fixed seed makes results reproducible; percentiles are already stable at the default 500 because the market model carries the statistical structure (correlated assets, fat tails, persistent inflation).
ℹ️This is education, not regulated financial advice. The figures here are illustrations generated from the information and assumptions you provide. They are not predictions, recommendations, or a statement of what you should do. Investment values can fall as well as rise, and you may get back less than you put in. Past performance does not indicate future results. For a personal recommendation, consult an FCA-regulated financial adviser. You can find one via the FCA Register or MoneyHelper.
What this tool is - and is not
It is: a self-directed cashflow modelling tool that projects your finances forward using your own figures, so you can explore "what if" scenarios and understand the mechanics of tax, pensions and retirement planning.
It is not: a regulated advice service. It does not know your full circumstances, does not recommend products, providers or transactions, and its output should not be acted on as if it were personal advice.
How projections are calculated
Each year, the model grows your assets by their assumed growth rate, applies your income and expenses, calculates Income Tax and National Insurance, then carries the resulting balance forward to the next year. Contributions are applied after growth (end-of-year basis). All figures are shown in nominal terms unless stated otherwise.
Tax is modelled as the year's total tax liability — Income Tax, National Insurance and, where investment sales are modelled, capital gains tax — charged in the year it arises. Hundred Summers does not model the timing of collection: there is no separate withholding step, and no following-year refund or self-assessment true-up. This mirrors how PAYE broadly works for UK employees, and keeps every chart (including the cashflow map) showing the same single tax figure. Tools built around other tax systems sometimes chart withholding and refunds as separate flows instead; if you owe or reclaim tax across year boundaries in real life, the annual totals here will still be right, but the timing may differ slightly.
The stress test runs a Monte Carlo simulation - many randomised return paths - to estimate how often your plan would succeed under varying market conditions. The success rate is the proportion of simulated paths in which your money lasts to your plan-end age. It is an illustration of sequencing risk, not a guarantee.
How the stress test varies the base assumptions. Your ordinary projection uses a single fixed growth rate for each asset. The Monte Carlo stress test keeps each asset's expected return exactly where you set it — each pension pot's random yearly return is centred on its own risk-profile or growth-rate figure, each property on its own growth rate, and savings accounts on theirs — but scatters every year's draw by a volatility (standard deviation) reflecting how bumpy that asset really is: 16% for equities, 6% for bonds and 8% for property, with each pension pot's volatility scaled by its equity share (a cautious pot swings less than an adventurous one). Because each year compounds into the next, the order in which good and bad years fall matters - an early loss in retirement hurts more than the same loss later. Running the whole plan hundreds of times captures this sequence-of-returns risk.
The market model behind the draws. Each simulated year is one correlated market event, not a set of independent coin flips. Equities, bonds, property and inflation are drawn together (equity–bond correlation 0.1, equity–property 0.5, bond–inflation -0.3), so the simulation can produce years like 1974 or 2022 — shares and bonds down with inflation up, together. Every holding shares the same market year by its asset composition: an equity ISA falls in the same year as an equity-heavy pension (the wrappers differ; the market doesn't), and cash accounts take no market shock at all. Return draws are Student-t distributed (8 degrees of freedom) rather than normal, so deep-loss years arrive at roughly their historical frequency instead of being ruled out by thin tails. Inflation is persistent — a high year tends to be followed by another (autocorrelation 0.7, long-run spread 1.5%) — and the simulated inflation path scales your living costs against the plan's expected inflation, so a multi-year cost-of-living squeeze is a scenario the test genuinely runs. The State Pension tracks the simulated inflation too (the triple lock guarantees at least CPI); DB indexation and annuity escalation keep your plan's own assumptions, a stated simplification. Tax and NI thresholds also keep your assumed indexation path rather than following each simulated inflation path: in a high-inflation simulation your spending rises but the tax bands don't keep pace, so those paths carry extra fiscal drag — mildly conservative, and arguably how governments actually behave in inflationary episodes. This model is validated against ~a century of market history in the test suite: its structure reproduces the record's inflation persistence, asset co-movement and tail weight, and in a classic retirement-drawdown backtest it sits deliberately on the conservative side of the realised record — real markets historically mean-reverted over long horizons, and this model does not assume that rescue will repeat. Success rates here read a few points lower than tools that treat each holding and each year as independent; that is the model being honest about risks the independent approach cannot see.
Same plan, same answer: the simulation is deterministic. The random market paths are drawn from a fixed seed, so every visit to the stress test replays the SAME set of simulated market histories. The success rate therefore never wobbles between runs: it moves only when your plan actually changes, and a change that cannot affect the cashflow test (renaming a profile, adding a debt-free property that is never drawn on) moves nothing. What varies between plans is how your money fares along those same market years — which is exactly the comparison a stress test should make. It also means the success rate, the fan chart and the per-year spending likelihood are counted from the same simulations and can never disagree with each other.
What the simulation deliberately simplifies. The stress test re-runs the full plan mechanics — employment windows, contributions, PCLS, annuity purchases, drawdown order, financial events, mortgages, downsizing, equity release, priority tiers — but it is a fast stochastic model, not a second copy of the detailed engine. Pension drawdown IS taxed: each year's pension withdrawal is grossed up against the tax bands it stacks onto (on top of salary, State Pension, DB and annuity income, which are taxed as before), so meeting a net spending need costs the simulation what it costs the detailed projection. Still simplified inside the simulation: capital gains tax on investment sales, savings-interest and dividend taxes are not mirrored, and the ISA subscription cap is not enforced (wrappers aren't taxed here, so which account holds an inflow cannot change the outcome) — the deterministic engine remains the authority on any single path, and the simulation's job is the SPREAD around it. DB pension indexation and annuity escalation follow your plan's assumptions rather than the simulated inflation, as noted above.
Two different ways of being wrong: the stress test vs the Outcome range. The master chart (Report → Chart) offers both, and they answer different questions. The stress test asks: even if my assumptions are right on average, how much do random market sequences scatter the outcome? It is probabilistic, and it applies to net worth only, because that is what the simulation tracks — which is why it appears as the Net Worth series' "stress test" state. The Outcome range asks: what if my assumptions themselves are wrong? It contains no randomness at all — the plan is re-projected through two alternative worlds, a pessimistic one (investment growth 1.5 percentage points lower, property 1 point lower, inflation and care inflation 1 point higher, every year) and an optimistic one with the same shifts reversed — and every drawn dataset is shaded across the envelope of the three worlds (the central plan is included because some figures, such as drawdown tax, do not move smoothly between worlds). No probabilities attach to the Outcome range; it is a scenario illustration. A plan that holds up at the pessimistic edge of the Outcome range and at the stress test's 10th percentile is robust to both ways of being wrong.
The couples stress test (on the Couples tab) runs every partner's plan through the same simulated market years — a shared sequence of good and bad years, as a real household would experience — and counts a simulation as a failure only when the household's combined unmet spending exceeds the partners' combined remaining pots and savings. It is slightly optimistic in assuming money can move freely between partners; year-by-year transfers are not modelled.
How best and worst cases are calculated. The tool does not hand-pick an optimistic or pessimistic set of assumptions. It runs the full plan hundreds of times - each a different random sequence of years - then, at every age, sorts all the resulting net-worth figures and reads off percentiles. The worst-case band is the 10th percentile (only 1 in 10 runs did worse), the median is the 50th percentile, and the best-case band is the 90th percentile (only 1 in 10 did better). The shaded 10th-90th range holds the middle 80% of outcomes, and the inner 25th-75th band the middle half. The spread you see comes entirely from varying the base return and inflation assumptions year by year - not from changing your inputs.
Tax assumptions (2024/25 England rates)
Personal Allowance
£12,570 (tapered above £100,000, gone at £125,140)
Basic rate (20%)
£12,571 - £50,270
Higher rate (40%)
£50,271 - £125,140
Additional rate (45%)
Above £125,140
Employee NI
8% between £12,570 and £50,270, 2% above
Pension annual allowance
£60,000 (editable in Plan Assumptions above), tapered by £1 for every £2 of adjusted income over £260,000 (down to a £10,000 floor); only applies if threshold income exceeds £200,000. Contributions above the allowance receive no tax relief in the model. Carry-forward: unused allowance from the previous three tax years (entered under Your Facts → Pensions) tops up the current year, consumed oldest-first; the projection then rolls its own three-year window forward. MPAA: from the year after the plan's first taxed pension withdrawal (UFPLS taxable element or crystallised drawdown income — a PCLS lump sum or annuity purchase alone does not trigger it), the allowance is capped at the £10,000 Money Purchase Annual Allowance. This bites when a role windowed past retirement keeps contributing while the pension is drawn; carry-forward stops applying and accruing from that point (the alternative-allowance split is not modelled). DB schemes: each pension can carry a survivor percentage (used by the Couples survivor analysis), a bridging income paid until State Pension age, and a commutation — a tax-free lump sum at the start age (consuming Lump Sum Allowance) in exchange for income reduced by lump ÷ commutation factor. Employee NI is charged on earnings until State Pension age (not your own retirement age); income tax and student-loan repayments follow earnings wherever they fall. Self-employed earnings (Income tab flag) pay Class 4 NI on profits (6% between £12,570 and £50,270, 2% above) instead of employee Class 1; the flag covers all earned income. Child benefit (children + youngest birth year on the Income tab) arrives as tax-free income until the youngest turns 18, reduced by the High Income Child Benefit Charge between £60,000 and £80,000 of income; modelled through working years. The marriage allowance (recipient side) applies as the ~£252/yr credit while no higher-rate tax is due.
Capital Gains Tax
18% (within basic-rate band) / 24% (above), after the £3,000 annual exempt amount. Applied to gains realised when drawing from General Investment Accounts. ISAs, cash and pensions are exempt.
Fill & recycle drawdown
An optional drawdown strategy (Pension Income tab): band-fill behaviour, plus in any retirement year whose taxable income sits below the higher-rate threshold, extra pension is drawn up to the top of the basic-rate band beyond spending needs, and the after-tax surplus is swept into savings — ISA first, within the annual ISA allowance, overflowing to a general investment account. The aim is to use cheap tax years (typically before State Pension and DB income begin) so later withdrawals avoid higher rates. The projection charges the extra tax in the year of the draw, loses the pension's tax-free compounding on the amount moved, and taxes subsequent GIA growth — so the outcome is shown honestly and is not always a win. This recycles taxable drawdown, not tax-free cash, so HMRC's PCLS-recycling rules are not engaged. Off by default.
Salary sacrifice
When switched on (Tax tab), the sacrificed amount reduces the salary on which income tax and employee NI are computed and flows into your pension as an employer contribution throughout your working years. It counts toward the annual allowance but is not double-relieved against taxable income. Sacrifice replaces your own employee contributions £-for-£ up to their total — the conversion real arrangements make — so pensions receive max(your contributions, sacrifice) plus employer money, never both in full; sacrifice beyond your own contributions is additional money in. Relative to an ordinary employee contribution the incremental benefit is the NI, since income-tax relief applies to both routes. No employer NI pass-on is assumed.
ISA allowance
£20,000 a year (editable in Plan Assumptions above), enforced across every route into ISA accounts — contributions, surplus, windfalls, transfers, sale proceeds and reinvested lump sums share one annual cap. Anything above it is diverted into a General Investment Account, where later gains attract CGT. ISA-to-ISA transfers do not use up the allowance.
Savings & dividend tax
Interest on non-ISA cash accounts (Premium Bonds excepted — prizes are tax-free) and on bond/cash holdings in a GIA is taxed at 20/40/45% above the Personal Savings Allowance (£1,000 basic-rate / £500 higher-rate / nil additional-rate), rising to 22/42/47% from April 2027 per the Autumn Budget 2025. Dividends on GIA equity (2% yield assumed; mixed funds 1% dividends + 1.5% interest, capped by the account's growth rate) are taxed at 10.75/35.75/39.35% (the April 2026 rates) above the £500 dividend allowance. UK-wide rates apply even under the Scottish regime, as in law. The income itself stays reinvested inside each account's growth rate — only the tax is charged to your cashflow. The £5,000 starting rate for savings is not modelled.
Band-fill drawdown (optional)
When selected on the Pension Income tab, each retirement year draws taxable pension income only up to the top of the basic-rate band (given that year's other taxable income), meeting the rest from savings/ISAs tax-free; pension above the band is used only if savings run out.
Tax wrappers
ISA/LISA growth and withdrawals are tax-free. Lifetime ISA: contributions capped at £4,000/yr (using part of the £20,000 overall ISA allowance) and only until 50; the 25% government bonus is added to what goes in; the balance is locked until 60, so the drawdown order skips it before then. Onshore and offshore bonds roll growth up inside the wrapper with a cumulative 5% p.a. tax-deferred withdrawal allowance on the original investment; gains beyond it are chargeable-event gains taxed as income — offshore at full rates, onshore top-sliced over the years held with a 20% basic-rate credit (a basic-rate taxpayer owes nothing further; the personal savings allowance interaction is not modelled). EIS/VCT holdings: 30% income-tax relief on new subscriptions (assumed actually invested, capped at the tax otherwise due), tax-free dividends and no CGT on disposal; the EIS three-year holding rule, loss relief and business-relief IHT treatment are not modelled — enter qualifying business relief on the IHT tab.
Risk questionnaires
Alongside attitude to risk and capacity for loss, the Risk tab carries a Knowledge & Experience self-assessment (six questions, banded Basic / Informed / Experienced) and a Sustainable Investing preference questionnaire (five questions, banded from no particular preference to strong preference). Both are educational documentation, not regulated appropriateness or suitability tests, and change no projection numbers; scores and bands appear on the Excel Risk Profile sheet. Each questionnaire also flags internally inconsistent answers - two responses at least three points apart on the 1-5 scale once at least half the questions are answered - as a prompt to re-read, not a verdict.
Income floor
The Pension Income tab's floor card compares the essential share of retirement spending (items not marked nice-to-have; the whole budget when none are marked) against guaranteed lifetime income - DB, State Pension and annuities - net of the tax due on that income alone, both measured in the first year everything is in payment. The purchase that would close a gap is quoted at the market annuity rate for the purchase age with the user's own annuity options, grossed up for basic-rate tax (a stated simplification).
Stress battery
The Stress Test tab's named battery re-runs the plan through the full deterministic engine under specific shocks: a 25% equity-weighted market fall today, all growth 2pp lower, inflation 2pp higher, stopping work three years early, living to 100, and paid care from five years before the Later Life age. Each is judged twice - the full budget, and essentials only (nice-to-have items given up first). Deterministic what-ifs on the plan's own assumptions; the Monte Carlo covers random market paths.
Per-year spending likelihood
The Stress Test tab reports, for every plan year, the share of simulated market paths in which that year's spending could be funded — the full budget and the essential budget (retirement items not marked nice-to-have) separately. The pass mark shown is essentials met in at least 95% of paths in every year. Counted from the same fixed-seed simulation as the success rate, so the two can never disagree.
Historical backtest
The Stress Test tab also replays the plan through every rolling window of annual market history from 1928 to 2023 (S&P 500 and US 10-year Treasury total returns from Aswath Damodaran's long-run dataset, US CPI from the BLS) — a US series used as a developed-market proxy, because UK data of that length is licensed; the stylised facts that matter (crashes, persistent inflation, co-movement) hold in both markets. Each window contributes its year-by-year DEVIATIONS from the record's own averages, layered onto the plan's own growth and inflation assumptions — history's shape, not its level — so the backtest tests sequence risk while the user's assumptions stay authoritative; because assumed returns typically sit below the record's realised average, the backtest can fail more windows than raw history did. In replay mode earned income, other income, DB pensions AND the tax and NI thresholds track the cumulative inflation surprise exactly as spending does (wages, DB indexation and tax bands broadly followed prices through the great inflations; without this the inflation replay dominates every result), while level annuities stay level. The record has no property series, so property carries only the inflation surprise. It is the single path history took, not a distribution — the Monte Carlo remains the primary stress test.
Goal-seek solvers
The Overview's “What would it take?” answers are solved on the full engine by binary search — most sustainable spending, earliest affordable retirement age, and the annual redirection needed to retire at a chosen age (spending less sweeps into savings automatically; the pension route adds the freed amount as a contribution, so tax relief usually makes it the smaller number). Each can also be judged at ≥85% simulation confidence: the fixed-seed Monte Carlo must succeed in at least 85% of simulated market paths, which is stricter than the single central projection. Asset headroom is the largest fraction by which pots and savings could fall today with every year still funded (property excluded — not drawable wealth in this model).
Expense priorities & recurring events
Financial events can repeat every N years (a car every 5, school fees each year of a course). Retirement expense items can be marked essential or nice-to-have; with the opt-in priority-tiers toggle (Expenses tab), a year the money cannot fully fund first gives up nice-to-have items — the reported shortfall then measures unfunded ESSENTIAL spending. Off (the default), the whole budget is one must-fund figure, exactly as before.
Pension tax-free cash
25%, capped by the £268,275 Lump Sum Allowance — taken either as an upfront lump sum (PCLS, which crystallises the pots so later withdrawals are fully taxable) or gradually when no lump sum is taken (UFPLS-style: 25% of each withdrawal tax-free until the allowance is used).
Pensions in the estate (April 2027)
From 6 April 2027 unused pension funds count into the taxable estate (Finance Act 2025). Hundred Summers applies this automatically: the per-year IHT estimate includes remaining pension pots for every projection year from 2027 onward, while a death assumed before then leaves them outside the estate.
Property income rates (April 2027)
From April 2027 property income has its own income tax rates, 2 percentage points above the main rates (22% / 42% / 47%) — Autumn Budget 2025. Hundred Summers charges this as a 2% surcharge on the taxed slice of income lines marked as property/rental (the top slice of non-savings income under the reform's ordering rules). Scottish rates on property income are devolved and not changed by this reform, so the surcharge applies outside Scotland only.
IHT nil-rate band
£325,000 (editable in Plan Assumptions above), frozen since 2009. Unused NRB transfers to a surviving spouse (entered on the Inheritance tab). PETs within 7 years of death erode the NRB before other assets — after the £3,000 annual gift exemption per gift year (carry-forward of one prior year's unused exemption is not modelled). Taper relief follows the statutory rule: it reduces only tax charged on the slice of gifting that exceeds the available NRB (gifts consumed in date order) — a gift fully inside the band gets no relief however old it is. Business & Agricultural Property Relief: from April 2026 the 100% rate applies to the first £1M of combined qualifying property, 50% beyond (AIM shares are not distinguished).
IHT residence nil-rate band
£175,000 (editable in Plan Assumptions above) when the main home passes to direct descendants — capped at the property's value and tapered £1 for £2 above a £2m estate. Unused RNRB also transfers to a surviving spouse.
All projections are computed in nominal (future) money — salaries, expenses and tax thresholds inflate through time. The 💷 toggle in the header can display everything in today's money instead: each year's figures are deflated at the tax-threshold inflation assumption (2.5% unless you change it), which makes distant years directly comparable with today but changes no underlying calculation.
Thresholds are assumed frozen at current levels for the life of the projection unless you change them. We classify each savings/investment account as cash, ISA or a General Investment Account (GIA) - based on its name, or you can set it explicitly - because only GIA gains are subject to CGT. Scottish income tax is fully modelled: set your region to Scotland on the Personal tab and the six Scottish bands (19% starter, 20% basic, 21% intermediate, 42% higher, 45% advanced, 48% top) are applied to non-savings income, while NI and CGT remain UK-wide as in reality. Tax rules change and your own position may differ.
Key growth & inflation assumptions
Plan-wide rates (inflation, care inflation, State Pension growth, tax threshold indexation, property growth, and DB pension indexation) are set in the Plan Assumptions section above and apply to all projections. Savings and investment accounts each have their own growth rate (editable in Your Facts → Assets & Debt). Pension pot growth is set by the risk profile you choose for each pot. All rates are nominal (before inflation). Defaults are conservative starting points, not forecasts.
Higher assumed growth rates produce more optimistic projections. Because small changes compound over decades, we encourage you to test lower growth and higher inflation to understand the range of possible outcomes.
Asset class default growth rates
Cash 2.0% | Bonds 4.0% | Equity 6.0% | Mixed/Multi-asset 5.0% — these are only starting points used to pre-fill the growth rate when you tag a savings/investment account with an asset class. They are broad, long-run indicative figures, not forecasts, and you can override them for any account.
Pension risk profiles
Each DC pension pot can be given a risk profile aligned to the five Attitude-to-Risk bands, which sets its growth rate automatically: Cautious (~20% equity, 3.5% growth) | Cautious-Moderate (~40%, 4.3%) | Moderate (~60%, 5.0%) | Moderately Adventurous (~80%, 5.6%) | Adventurous (~100%, 6.5%). Growth rates are a blend of long-run equity (~6%), bond (~4%) and cash (~2%) assumptions weighted by the profile's equity allocation. These are broad indicative figures, not forecasts; you can still override any pot's growth rate manually by selecting 'Custom'. The chosen equity allocation is also what the Investment Portfolio & Risk assessment uses to weight each pension's market-risk exposure.
Portfolio risk assessment
The Investment Portfolio & Risk figure is a value-weighted equity-equivalent exposure across your savings/investment accounts (by asset class) and your DC pensions (by their risk profile's equity allocation). Property, defined-benefit pensions and the state pension are excluded. It is an educational comparison against your Attitude to Risk, not a personal recommendation.
Suggested allocation
Alongside the assessment, the ATR view shows the broad industry-practice asset mix for your (capacity-capped) risk profile — 20/55/25 equities/bonds/cash for Cautious through 100/0/0 for Adventurous — next to where your portfolio is now, with the amount that would move each class to the suggested share. For the comparison, mixed funds are counted 55% equities / 45% bonds (mirroring the risk assessment's weighting) and each pension pot by its chosen risk profile's equity share. A shape, not a model portfolio or fund selection — Hundred Summers holds no fund data, and reshaping is best done inside existing tax wrappers.
Loss-of-earnings what-if
The Risk tab's Protection section re-runs the whole plan with earnings stopped from a chosen age — permanently, or for a chosen number of years with work resuming at the salary it stopped on (progression paused during the break, growth restarting on return; future roles that start after the recovery are unaffected). With cover included, critical-illness lump sums arrive in the shock year and income-protection benefits pay tax-free after each policy's deferral period (a part-year deferral scales the first benefit year), ending at the policy's own end or the return to work, whichever is first. Tax, NI and pension contributions all stop with the pay, so the knock-ons are real.
Savings vs pensions drawdown split
How each retirement year's withdrawal is divided between savings and pensions. This plan: In order: savings/ISA, then pensions — draining each before the next. Set it with the blend slider on the Pension Income tab; pension withdrawals are taxable income, savings withdrawals are not, so the split changes your tax bill.
Working-year shortfalls
A working year where total outgoings (spending, tax, pension contributions and debt repayments) exceed income is funded by drawing the gap from your savings accounts, most-liquid first — shown as a savings drawdown in the charts, exactly as in retirement. Pensions are never tapped for this (they are usually inaccessible before 55). If savings run out, the remaining gap is recorded as that year's unfunded spending — it fails the plan (the Overview's funding goals, the event goal cards and the stress test all read this same verdict), because the plan cannot borrow and cannot touch pensions early, however large the pots. This matters for decisions like phased retirement: cutting your salary before your costs fall genuinely spends your savings.
Liquidity-based drawdown order
Within savings, accounts are drawn most-liquid-first: instant access, then notice/short-term, then illiquid/locked — regardless of the order you entered them in. Within the same liquidity tier, your original entry order is preserved. This reflects how withdrawals realistically happen, but is still a simplification — it doesn't account for product-specific penalties, fixed-term maturity dates, or your own preferences about which accounts to draw from first.
State pension basis & deferral
This plan: 0 qualifying years + 25 future working years + 10 gap years, capped at 35. The figure can be entered directly, or derived from your NI record on the Tax tab (35 qualifying years for the full new State Pension, minimum 10, pro-rata between — including working years still ahead and any gap years you plan to buy). Deferring adds a permanent 5.8% for each full year deferred and shifts the start age accordingly.
State pension indexation
The resolved state pension amount is treated as today's figure and indexed at the stated growth rate from today, becoming payable at the resolved start age (State Pension age plus any deferral). This keeps it consistent with the rest of the model, where salary, expenses and rental income all grow in nominal terms from today.
Income tax & NI threshold indexation
Tax and NI thresholds are not assumed static. They are held at 2024/25 levels through the current freeze to 5 April 2031 (extended from 2028 by the Autumn Budget 2025), then indexed each year at your chosen rate (2.5%, editable in Plan Assumptions above). During the freeze, rising pay pushes more income into higher bands (fiscal drag); once thresholds index in line with pay, your effective tax rate roughly stabilises rather than drifting upward forever. The £100,000 personal-allowance taper point stays frozen throughout, as it has since 2010.
Tax rates over time
Thresholds move over time (see above), but the tax rates and percentages themselves are held constant at 2024/25 levels for the whole projection: income tax at 20% / 40% / 45%, the 60% effective band in the £100,000–£125,140 personal-allowance taper, employee NI at 8% / 2%, CGT at 18% / 24%, the 25% tax-free pension lump sum, and IHT at 40%. A future Chancellor may change any of these rates, add or remove bands, or alter reliefs — changes no model can predict. Because thresholds move but rates do not, your effective (average) tax rate still changes year to year as income moves through the bands, even though the headline rates are fixed. Treat the tax figures as illustrative under today's rate structure, not a forecast of future tax law.
Liability amortisation
Liabilities with a monthly payment amortise each year: interest accrues at the stated rate, then twelve months of payments are deducted, floored at zero once cleared. Repayments are assumed to already be part of your stated living expenses, so they are not double-counted. Liabilities without a stated payment simply compound at their interest rate — a conservative treatment of unmanaged debt.
External reference data
Where the model uses figures from outside your own inputs, they come from the following public sources. We try to keep these current, but rates, thresholds and tables are reviewed periodically (typically each tax year) and may lag the latest published figures — always check the primary source for the most current numbers.
Income Tax bands & Personal Allowance
HM Revenue & Customs, Income Tax rates and Personal Allowances, 2024/25 tax year. gov.uk/income-tax-rates
National Insurance rates
HM Revenue & Customs, National Insurance rates and categories, 2024/25 tax year. gov.uk/national-insurance-rates-letters
Pension annual allowance & taper
HM Revenue & Customs, Pensions tax manual (PTM); GOV.UK pension allowances guidance, 2024/25.
Lump Sum Allowance (PCLS cap, £268,275)
HM Revenue & Customs, abolition of the Lifetime Allowance and introduction of the Lump Sum Allowance, effective 6 April 2024.
Capital Gains Tax rates & annual exempt amount
HM Revenue & Customs, Capital Gains Tax rates, 2024/25 tax year (reduced annual exempt amount of £3,000 from April 2024). gov.uk/capital-gains-tax/rates
Inheritance Tax nil-rate bands
HM Revenue & Customs, Inheritance Tax thresholds and rates, frozen at £325,000 (nil-rate band) and £175,000 (residence nil-rate band) until April 2030. gov.uk/inheritance-tax
State Pension amount & qualifying years
Department for Work & Pensions, new State Pension rates 2026/27 (full rate £241.30/week); 35 qualifying National Insurance years for the full amount. gov.uk/new-state-pension
Voluntary NI contribution cost
HM Revenue & Customs / DWP, Class 3 voluntary National Insurance contribution rates, 2024/25.
Annuity rates
Indicative market-average rates compiled from published UK annuity quote comparisons (2025/26), for a healthy non-smoker. Not from a single provider — real quotes vary and should be obtained via the Open Market Option. moneyhelper.org.uk/annuities
Baseline life expectancy
Office for National Statistics life tables, life expectancy at age 65 by sex at birth (84.5 male, 87.2 female). The health-profile estimate starts from the baseline for your recorded sex; if you'd rather not say, the longer female baseline is used — the safer planning assumption. ons.gov.uk - search 'National life tables'
Retirement spending benchmarks
Pensions and Lifetime Savings Association (PLSA), Retirement Living Standards, used as a reference point only where mentioned in guidance text - not used directly in your projection unless you enter these figures yourself. retirementlivingstandards.org.uk
Long-term care costs by care type
Indicative UK annual costs used for the Later Life phase and the care scenario: in-home care £65,000, residential care home £57,000, nursing home £87,000. These are midpoints of published ranges from Laing & Buisson Care Cost Benchmarks, Age UK, and MoneyHelper (2024/25). Actual fees vary widely by region and provider - always obtain local quotes. laingbuisson.com - ageuk.org.uk - moneyhelper.org.uk
Care cost inflation
Care fees have historically risen faster than general (CPI) inflation. The model defaults to 4% a year for care costs versus around 2.5% for other retirement spending, based on Laing & Buisson and ONS care-price trends. This rate is editable in the Longevity tab.
None of these sources endorse this tool, and we are not affiliated with HMRC, DWP, ONS, the PLSA, Laing & Buisson, Age UK, or any annuity or care provider. Where a figure has likely changed since this was last reviewed, your own entries always take precedence over any built-in default.
Limitations you should be aware of
The model simplifies a complex reality. While it now models Capital Gains Tax on investment disposals and the tapered pension annual allowance, it does not capture every tax nuance (for example, CGT on second-property sales — an Asset Sale event credits the full sale amount to savings without a CGT deduction — or every allowance interaction), assumes you remain UK-resident, and cannot account for changes in legislation, your health, employment, or family circumstances. It assumes the figures you entered are accurate and complete.
Projections are only as good as their inputs and assumptions. They illustrate possibilities; they do not predict your actual future.
Your data
Your plan lives on your own device, in this browser, so you can return to it. It is never uploaded to us. Because it lives in the browser, clearing your browser data — or switching to a different device or browser — means it won't automatically be there.
Automatic backup keeps a copy without any manual saving: set it up once in ⚙️ Settings, choose where the file lives, and Hundred Summers rewrites it every time your plan changes — and loads a newer version automatically at startup. Pick a folder that syncs with your cloud storage (Google Drive, OneDrive, iCloud or Dropbox) and the same plan follows you between your phone and your laptop. A "Change location" button lets you move it at any time. The file is protected automatically with AES-256 encryption using a key tied to your account — nothing to type, and any device you sign into can read it. (A file you previously protected with a passphrase keeps that passphrase — each device asks for it once, and there is no recovery without it.) Browser support for choosing a live file location is currently limited to Chromium-based browsers (Chrome, Edge) — elsewhere, use the manual save below. After a browser restart you may be asked to reconnect the file — a single tap.
Alongside it, Export snapshot (in the profile menu) creates a dated copy of all your profiles — an archive of the plan as it stood that day, useful before big changes, at year-end, or as protection if the live backup file is ever damaged. It's also the way to share a copy without linking anyone to your live file, and the primary save method on devices without auto-backup support. On most browsers you can choose exactly where it goes and what to call it. You can save it wherever you like — and if you wish, you can save it into a cloud-synced folder such as Google Drive, OneDrive, iCloud or Dropbox, so it's backed up and available on your other devices. That is entirely at your discretion; Hundred Summers never sends the file anywhere itself. Keep in mind the file contains detailed personal financial information, so store it somewhere you trust, and remember the same if you share an exported report.
When saving a snapshot, you can optionally protect the file with a passphrase: it is then encrypted with AES-256 (the key derived from your passphrase) before it leaves the app, so the file is unreadable without it — including to us. There is no recovery if you forget the passphrase, so choose one you'll remember. Left blank, the snapshot saves as plain JSON so it can be restored anywhere — including by an adviser you send it to, or on a device where you can't sign in.
Use Import / restore to bring any saved file back in — an older snapshot, your auto-backup file on a device that can't connect to it directly, or after clearing your browser. Encrypted backups are detected automatically: account-protected files unlock silently when you're signed in with the account that made them, and passphrase-protected files ask for the passphrase. Restoring while auto-backup is connected also writes the restored plan back to your live file.
The single, optional exception to on-device processing is the Premium AI Copilot: when you ask it a question, the plan summary needed to answer (never your name) is processed securely by our AI provider, with your consent, and is never used to train AI models. If you never use the Copilot, nothing ever leaves your device. Full details are in the Privacy Policy.
Getting regulated advice
If you want a personal recommendation - someone to tell you what is right for your circumstances and take responsibility for that advice - you need an FCA-regulated financial adviser. Free, impartial guidance is also available from MoneyHelper (moneyhelper.org.uk), a government-backed service. You can check that any adviser is authorised on the FCA Register (register.fca.org.uk).