Hundred Summers

Validation pack

Standard cases for the parts of the plan that follow fixed rules — income tax in England, Wales, Northern Ireland and Scotland, National Insurance, savings and dividend tax, Capital Gains Tax, pension allowances and tax-free cash, the State Pension, annuities and inheritance tax. Each is worked by hand from the official rule, step by step, and set beside the figure Hundred Summers' own engine produces for the same inputs. The engine column is computed when the site is built, and the build fails if any case differs by more than £1.00 — so this page cannot drift from the engine it describes.

30 cases, 2026/27 rules: 30 of 30 agree to within £1.00.

Download every case with its steps, figures and source: validation-pack.csv (spreadsheet) or validation-pack.json. Found a case you think is wrong? Tell us at contact@hundredsummers.co.uk.

Income tax: England, Wales and Northern Ireland

Salary £30,000
  1. £30,000 − £12,570 personal allowance = £17,430 taxable
  2. £17,430 at 20% = £3,486.00
Worked by hand: £3,486.00Engine: £3,486.00Difference: £0.00
Projection, first year: income tax. Rule: gov.uk: Income Tax rates and Personal Allowances.
Salary £60,000
  1. £60,000 − £12,570 = £47,430 taxable
  2. Basic rate: £37,700 at 20% = £7,540.00
  3. Higher rate: £9,730 at 40% = £3,892.00
  4. Total £11,432.00
Worked by hand: £11,432.00Engine: £11,432.00Difference: £0.00
Projection, first year: income tax. Rule: gov.uk: Income Tax rates and Personal Allowances.
Salary £110,000: personal allowance tapered
  1. Allowance falls £1 for every £2 over £100,000: £12,570 − £5,000 = £7,570
  2. £110,000 − £7,570 = £102,430 taxable
  3. Basic rate: £37,700 at 20% = £7,540.00
  4. Higher rate: £64,730 at 40% = £25,892.00
  5. Total £33,432.00
Worked by hand: £33,432.00Engine: £33,432.00Difference: £0.00
Projection, first year: income tax. Rule: gov.uk: Income Tax rates: income over £100,000.
Salary £150,000: no personal allowance
  1. No personal allowance above £125,140
  2. Basic rate: £37,700 at 20% = £7,540.00
  3. Higher rate: £125,140 − £37,700 = £87,440 at 40% = £34,976.00
  4. Additional rate: £150,000 − £125,140 = £24,860 at 45% = £11,187.00
  5. Total £53,703.00
Worked by hand: £53,703.00Engine: £53,703.00Difference: £0.00
Projection, first year: income tax. Rule: gov.uk: Income Tax rates: income over £100,000.

Income tax: Scotland

Salary £50,000, Scottish taxpayer
  1. Starter £12,571–£16,537: £3,967 at 19% = £753.73
  2. Basic £16,538–£29,526: £12,989 at 20% = £2,597.80
  3. Intermediate £29,527–£43,662: £14,136 at 21% = £2,968.56
  4. Higher £43,663–£50,000: £6,338 at 42% = £2,661.96
  5. Total £8,982.05
Worked by hand: £8,982.05Engine: £8,982.00Difference: −£0.05
Projection, first year: income tax. Rule: gov.uk: Scottish Income Tax 2026 to 2027.
Salary £80,000, Scottish taxpayer
  1. Starter, basic and intermediate bands as above: £753.73 + £2,597.80 + £2,968.56 = £6,320.09
  2. Higher £43,663–£75,000: £31,338 at 42% = £13,161.96
  3. Advanced £75,001–£80,000: £5,000 at 45% = £2,250.00
  4. Total £21,732.05
Worked by hand: £21,732.05Engine: £21,732.00Difference: −£0.05
Projection, first year: income tax. Rule: gov.uk: Scottish Income Tax 2026 to 2027.

National Insurance

Employee, salary £30,000 (Class 1)
  1. £30,000 − £12,570 primary threshold = £17,430
  2. £17,430 at 8% = £1,394.40
Worked by hand: £1,394.40Engine: £1,394.00Difference: −£0.40
Projection, first year: employee NI. Rule: gov.uk: National Insurance rates and categories.
Employee, salary £60,000 (Class 1)
  1. £12,570 to £50,270: £37,700 at 8% = £3,016.00
  2. Above £50,270: £9,730 at 2% = £194.60
  3. Total £3,210.60
Worked by hand: £3,210.60Engine: £3,211.00Difference: £0.40
Projection, first year: employee NI. Rule: gov.uk: National Insurance rates and categories.
Self-employed, profits £40,000 (Class 4)
  1. £40,000 − £12,570 lower profits limit = £27,430
  2. £27,430 at 6% = £1,645.80
Worked by hand: £1,645.80Engine: £1,646.00Difference: £0.20
Projection, first year: NI. Rule: gov.uk: Self-employed National Insurance rates.

Savings and dividend tax

Wages £16,000, savings interest £3,000
  1. Other income above the personal allowance: £16,000 − £12,570 = £3,430
  2. Starting rate for savings left: £5,000 − £3,430 = £1,570 at 0%
  3. Personal Savings Allowance (basic-rate taxpayer): £1,000 at 0%
  4. Remaining £3,000 − £1,570 − £1,000 = £430 at 20% = £86.00
Worked by hand: £86.00Engine: £86.00Difference: £0.00
Engine: calcSavingsDividendTax (as the projection calls it). Rule: gov.uk: Tax on savings interest: how much is tax-free. gov.uk's own worked example (£16,000 of wages leaves £1,570 of starting rate), extended with more interest.
Salary £40,000, dividends £10,000
  1. £500 dividend allowance at 0%, leaving £9,500
  2. Basic-rate band left: £50,270 − £40,000 = £10,270, so all £9,500 is basic rate
  3. £9,500 at 10.75% = £1,021.25
Worked by hand: £1,021.25Engine: £1,021.25Difference: £0.00
Engine: calcSavingsDividendTax (as the projection calls it). Rule: gov.uk: Tax on dividends.

Capital Gains Tax

Gain £20,000, income £40,000
  1. £20,000 − £3,000 annual exempt amount = £17,000 taxable gain
  2. Basic-rate band left: £37,700 − (£40,000 − £12,570) = £10,270 at 18% = £1,848.60
  3. The other £6,730 at 24% = £1,615.20
  4. Total £3,463.80
Worked by hand: £3,463.80Engine: £3,464.00Difference: £0.20
Engine: calcCGT (as the projection calls it). Rule: gov.uk: Capital Gains Tax rates and allowances.
Gain £50,000, income £5,000
  1. £50,000 − £3,000 = £47,000 taxable gain
  2. Income is below the personal allowance, but unused allowance cannot be set against gains: the whole £37,700 basic-rate band is left, no more
  3. £37,700 at 18% = £6,786.00
  4. £9,300 at 24% = £2,232.00
  5. Total £9,018.00
Worked by hand: £9,018.00Engine: £9,018.00Difference: £0.00
Engine: calcCGT (as the projection calls it). Rule: gov.uk: Capital Gains Tax rates and allowances.
Selling a let property: £150,000 gain, no other income
  1. Bought £150,000, sold £300,000: £150,000 gain; not the main home, so no private residence relief
  2. £150,000 − £3,000 = £147,000 taxable gain
  3. £37,700 at 18% = £6,786.00
  4. £109,300 at 24% = £26,232.00
  5. Total £33,018.00
Worked by hand: £33,018.00Engine: £33,018.00Difference: £0.00
Projection: CGT charged in the sale year. Rule: gov.uk: Capital Gains Tax rates and allowances.

Pensions: allowances and tax-free cash

Tapered annual allowance: adjusted income £300,000
  1. Threshold income £220,000 is over £200,000, so the taper applies
  2. Allowance falls £1 for every £2 of adjusted income over £260,000: (£300,000 − £260,000) ÷ 2 = £20,000
  3. £60,000 − £20,000 = £40,000
Worked by hand: £40,000.00Engine: £40,000.00Difference: £0.00
Engine: calcTaperedAnnualAllowance. Rule: gov.uk: Tax on your private pension: annual allowance.
Tapered annual allowance: adjusted income £400,000
  1. Reduction (£400,000 − £260,000) ÷ 2 = £70,000 would take it below zero
  2. The allowance never falls below the £10,000 minimum
Worked by hand: £10,000.00Engine: £10,000.00Difference: £0.00
Engine: calcTaperedAnnualAllowance. Rule: gov.uk: Tax on your private pension: annual allowance.
Tax-free lump sum from a £1,200,000 pot
  1. A quarter of the pot: £1,200,000 × 25% = £300,000
  2. Capped by the £268,275 Lump Sum Allowance
  3. Tax-free cash £268,275
Worked by hand: £268,275.00Engine: £268,275.00Difference: £0.00
Projection: tax-free lump sum taken at 60. Rule: gov.uk: Tax when you get a pension: lump sum allowance.
Final-salary pension £20,000, lump sum asked for £100,000 at 12:1
  1. Tax-free cash is at most 25% of (20 × remaining pension + lump sum)
  2. With lump L at 12:1 the pension left is £20,000 − L ÷ 12, so L ≤ 25% × (20 × (£20,000 − L ÷ 12) + L)
  3. L ≤ £100,000 ÷ (0.75 + 5 ÷ 12) = £85,714.29
  4. The £100,000 asked for is capped at £85,714.29; pension given up £7,142.86
Worked by hand: £85,714.29Engine: £85,714.29Difference: £0.00
Engine: dbPermittedLump / dbCommutedLump (as the projection applies them). Rule: HMRC Pensions Tax Manual: PCLS applicable amount (PTM063240).
Final-salary pension £20,000, lump sum £60,000 at 12:1
  1. Permitted maximum as above: £85,714.29
  2. £60,000 is within it and is paid in full; pension given up £60,000 ÷ 12 = £5,000, leaving £15,000
Worked by hand: £60,000.00Engine: £60,000.00Difference: £0.00
Engine: dbPermittedLump. Rule: HMRC Pensions Tax Manual: PCLS applicable amount (PTM063240).

State Pension

35 qualifying years
  1. Full new State Pension £241.30 a week
  2. × 52 = £12,547.60 a year
Worked by hand: £12,547.60Engine: £12,548.00Difference: £0.40
Engine: resolveStatePensionAnnual. Rule: gov.uk: The new State Pension. The engine holds the annual figure rounded to the pound (£12,548).
20 qualifying years (record from April 2016)
  1. 20 of the 35 years: £241.30 × 20 ÷ 35 = £137.89 a week (to the penny)
  2. × 52 = £7,170.28 a year
Worked by hand: £7,170.28Engine: £7,170.00Difference: −£0.28
Engine: resolveStatePensionAnnual. Rule: gov.uk: The new State Pension. Applies to a record that starts after April 2016; earlier records use the transitional starting amount, which the plan takes from your forecast if you enter it.
9 qualifying years
  1. At least 10 qualifying years are needed for any new State Pension
  2. Nothing is payable
Worked by hand: £0.00Engine: £0.00Difference: £0.00
Engine: resolveStatePensionAnnual. Rule: gov.uk: The new State Pension.
Full State Pension deferred 52 weeks
  1. gov.uk's example: deferring 52 weeks adds £13.99 a week (5.8% of £241.30)
  2. £241.30 + £13.99 = £255.29 a week
  3. × 52 = £13,275.08 a year
Worked by hand: £13,275.08Engine: £13,276.00Difference: £0.92
Engine: resolveStatePensionAnnual. Rule: gov.uk: Delay (defer) your State Pension. The rule is 1% for every 9 weeks, which is just under 5.8% a year (5.78%, £13.94 a week); gov.uk's example and the plan's editable default both use 5.8%.

Annuity

£200,000 pot at 65, level, single life
  1. Published market-average rate at 65 for a level, single-life annuity with no guarantee: 7.1%
  2. £200,000 × 7.1% = £14,200 a year
Worked by hand: £14,200.00Engine: £14,200.00Difference: £0.00
Engine: calcAnnuity. Rule: Hundred Summers Methodology: annuity rates (published assumption). Annuity rates are a published assumption, not a rule: this case checks the plan applies the rate it publishes. A real quote replaces it.

Inheritance tax

Estate £800,000, home left to children
  1. Nil-rate band £325,000 and residence nil-rate band £175,000 (home worth £400,000)
  2. £800,000 − £325,000 − £175,000 = £300,000 taxable
  3. £300,000 at 40% = £120,000
Worked by hand: £120,000.00Engine: £120,000.00Difference: £0.00
Engine: calcIHT. Rule: gov.uk: How Inheritance Tax works: thresholds.
Second death, £1,600,000 estate, both bands transferred
  1. Nil-rate bands £325,000 × 2 = £650,000
  2. Residence bands £175,000 × 2 = £350,000 (home worth £600,000, left to children)
  3. £1,600,000 − £650,000 − £350,000 = £600,000 at 40% = £240,000
Worked by hand: £240,000.00Engine: £240,000.00Difference: £0.00
Engine: calcIHT. Rule: gov.uk: How Inheritance Tax works: thresholds.
Estate £2,200,000: residence band tapered
  1. Residence band falls £1 for every £2 over £2,000,000: £175,000 − £100,000 = £75,000
  2. £2,200,000 − £325,000 − £75,000 = £1,800,000 at 40% = £720,000
Worked by hand: £720,000.00Engine: £720,000.00Difference: £0.00
Engine: calcIHT. Rule: gov.uk: Inheritance Tax: residence nil rate band.
Estate £2,400,000 including £400,000 of business property
  1. The taper looks at the estate BEFORE reliefs: £2,400,000 is £400,000 over £2,000,000, so the residence band tapers by £200,000, to nil
  2. Business relief at 100% (within the £2.5 million cap): £2,400,000 − £400,000 = £2,000,000
  3. £2,000,000 − £325,000 = £1,675,000 at 40% = £670,000
Worked by hand: £670,000.00Engine: £670,000.00Difference: £0.00
Engine: calcIHT. Rule: gov.uk: Inheritance Tax: residence nil rate band.
HMRC's example: £750,000 estate, £50,000 to charity
  1. Chargeable estate £750,000 − £50,000 = £700,000
  2. Baseline amount: £700,000 − £325,000 nil-rate band + £50,000 legacy = £425,000
  3. £50,000 is at least 10% of £425,000, so the 36% rate applies
  4. £700,000 − £325,000 = £375,000 at 36% = £135,000
Worked by hand: £135,000.00Engine: £135,000.00Difference: £0.00
Engine: calcIHT. Rule: HMRC Inheritance Tax Manual: baseline amount (IHTM45009–45011). HMRC's own worked example (IHTM45010).
HMRC's example: the same estate after a £150,000 gift four years earlier
  1. The £150,000 gift (after the £3,000 annual exemption) uses £150,000 of the nil-rate band: £175,000 left
  2. Baseline amount: £700,000 − £175,000 + £50,000 = £575,000
  3. £50,000 is less than 10% (£57,500), so the rate stays 40%
  4. £700,000 − £175,000 = £525,000 at 40% = £210,000
Worked by hand: £210,000.00Engine: £210,000.00Difference: £0.00
Engine: calcIHT. Rule: HMRC Inheritance Tax Manual: baseline amount (IHTM45009–45011). HMRC's own worked example (IHTM45011). The gift sits inside the nil-rate band, so it bears no tax and gets no taper relief.

What this does not show

These cases check that the engine applies each rule correctly in a single year. They do not check the assumptions a projection rests on — investment growth, inflation, annuity rates, how long you live — which are published, editable and stress-tested rather than right or wrong; nor do they check how the rules combine over a lifetime, which the engine's balance-sheet reconciliation (every pound accounted for, every year, on every plan) and its cross-check against an adviser tool cover. See the Methodology for both.

Education, not advice. Figures use the 2026/27 rules for England, Wales and Northern Ireland unless a case says Scotland; they show how the rules apply, not what you should do.