Hundred SummersHow much do I need to retire? Solved, not guessed
Not 25× anything: a binary search over pot size where every candidate is tested by a full year-by-year UK projection; income tax on withdrawals, the State Pension from your late 60s, real drawdown mechanics. Your figures never leave your browser.
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Worked example
Computed when this page was built by the same engine that runs the calculator above, so the figures below and the live tool can never disagree. Change any input above to see your own.
| Inputs | |
|---|---|
| Retire at | 65 |
| Spending a year (today's money) | £30,000 |
| Growth | 5.0% |
| Include State Pension | Yes |
| Plan to age | 95 |
| Results | |
|---|---|
| Pot needed, solved by projection | £475,000 |
| The 25× rule of thumb | £750,000 |
| Actual multiple of spending | 15.8× |
The next question
When could I stop work? →When can I retire?
Or answer it with everything else: the full Hundred Summers plan connects your pay, pensions, savings, property, tax and spending year by year, and stress-tests them across 500 simulated market histories.
Read the guides
- The 4% rule: what it misses for UK retirees →Where the famous retirement withdrawal rule comes from, why its US assumptions travel badly to the UK, and what a real projection tests instead: tax, the State Pension, and the market sequences that actually broke retirements.
- How much do I need to retire in the UK? Solved, not guessed →Why 25× spending, £500k-for-everyone and half-your-age rules all miss, what actually moves the number (tax, the State Pension, your dates), and how a real projection solves it.
Why the multiple rules mislead
The popular answers: 25× spending, half your age as a percentage, £500k for everyone; all skip the same three things. Tax: withdrawals beyond the tax-free elements are income, so a gross pot funds less net spending than it looks. The State Pension: ~£12,500 a year, inflation-protected, from your late 60s; over a 30-year retirement it quietly does £300,000+ of the job. Your dates: retiring at 55 versus 68, and planning to 85 versus 100, moves the answer by hundreds of thousands.
What this calculator does instead
It solves for the smallest pot whose full projection funds every year: each candidate pot is run through the same engine as the Hundred Summers app (spending inflated year by year, withdrawals grossed up for the actual tax bands, the State Pension arriving on schedule), and a binary search narrows to the answer. The result usually lands meaningfully away from 25×, in a direction the rule can't predict.
The number is still a steady-growth answer. The full Hundred Summers plan stress-tests your own figure through thousands of simulated markets and every historical sequence since 1928, and models your real accounts, spending phases, and everything else this one-pot page simplifies away.