Hundred SummersWhen can I retire? Solved by projection, not a rule of thumb
Your pension, ISA savings and ongoing contributions, tested age by age: the calculator runs the Hundred Summers app's own earliest-retirement solver, projecting every year of each candidate retirement with UK income tax on withdrawals and the State Pension, and returns the youngest age at which every year funds. 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 | |
|---|---|
| Age | 45 |
| Pension pot / paid in a year | £250,000 / £12,000 |
| ISA / paid in a year | £50,000 / £5,000 |
| Spending a year in retirement | £28,000 |
| Growth | 5.0% |
| Plan to | 95 |
| Results | |
|---|---|
| Earliest retirement age the projection supports | 58 |
| Ages tested up to | 74 |
The next question
Does everything else in my life change the answer? →
Only the whole picture answers that: 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
- FIRE in the UK: what the American playbook misses →The 25× rule and savings-rate maths transfer; the mechanics don't. The pension access age bridge, ISA-vs-pension sequencing, UK tax on the way out, and where Coast and Barista FI fit: the honest UK version.
- 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.
- Inheriting money: the order of operations →A lump sum arrives: inheritance, redundancy, a house sale. The unhurried sequence: debt, buffer, wrappers, the tax on what the money earns next, and the £2,880 trick for a non-earning partner.
How the answer is found
Most retirement-age calculators divide your pot by a spending multiple. This one does what the Hundred Summers app does: for each candidate age it projects every year of your plan (contributions until that age, then drawdown with income tax grossed up properly, the State Pension arriving on schedule, growth compounding on what remains), and asks whether any year fails to fund. A binary search then finds the youngest age where none does.
The result moves honestly with your inputs. More ISA saving buys retirement before pension access; the State Pension toggle shows how much of the answer it quietly carries; the plan-to age prices longevity. If the answer is “not by 74”, the plan needs more saving or less spending: better to know now. Related: how much do I need to retire? and the FIRE calculator.