FIRE Age Calculator
A full year-by-year simulation showing when work could become optional — real UK tax bands, pension access-age locking, and monthly mortgage amortization.
How this calculator works
Rather than solving a formula, the calculator tests every possible retirement age one at a time — running a full year-by-year simulation of your salary, spending, tax, mortgage, and account balances for each one — and returns the earliest age that clears two bars: the money lasts all the way to your life expectancy, and your first year of withdrawals stays at or below a 4% safe withdrawal rate. An age that only survives by drawing down faster than that doesn't count as a real answer.
For the full breakdown of every rule — nominal-vs-real handling, the decumulation order, and how pension locking works — see How the FIRE Age Calculator works.
Worked example
Take someone aged 35 earning £60,000 a year, planning to spend £28,000 a year in retirement. They hold £10,000 in cash, £30,000 in an ISA, and £50,000 in a pension (contributing £500 a month), own a £300,000 property with £180,000 left on a 4% mortgage over 20 years, growth assumed at 6%, and a full State Pension from age 67.
Running the simulation for every retirement age from 36 onward, the earliest one that both survives to life expectancy and keeps its first year of withdrawals at a safe 4% or under is age 66 — later than the point where the money technically doesn't run out, because retiring earlier than that only survives by drawing down faster than a safe margin allows.
Frequently asked questions
Why does it run a simulation instead of using a formula?
Because the things that decide your real retirement age change year to year — UK tax bands, a mortgage that eventually gets paid off, care costs that kick in later, a State Pension that starts at a fixed age. The calculator runs a full year-by-year simulation from your current age to your life expectancy, then repeats it for every possible retirement age from next year onward, and reports the earliest one that both makes it all the way to your life expectancy without running out of money and keeps its first year of withdrawals at or below a 4% safe withdrawal rate — surviving on paper isn't enough on its own if it only works by drawing down dangerously fast.
How does pension access-age locking work?
Your pension balance counts toward your net worth from day one, but the simulation will not draw a single pound from it before your chosen access age (57 by default — the UK's earliest normal private-pension access age from 2028). If your other accounts run dry before then, the plan is marked as not surviving, even if the pension itself is large.
Does it account for real UK income tax and National Insurance?
Yes. Take-home pay each working year is computed from your gross salary using real UK income tax and National Insurance bands, including the personal allowance taper above £100,000 — not a flat estimate. Retirement income is taxed too: pension withdrawals beyond the 25% tax-free element, your State Pension, and any DB pension are all taxed as income (no National Insurance on any of them, matching real UK rules) before they count toward covering your spending. Cash, ISA, and LISA withdrawals are genuinely tax-free and stay untaxed; GIA capital gains tax isn't modelled, since the calculator doesn't track cost basis.
What order does it draw money down from in retirement?
Cheapest tax consequence first: cash, then your GIA, then your ISA, then your LISA once you've turned 60, then your pension once you've reached your access age, and finally property — only if you've opted to include it as a last-resort backstop, and only once everything else is exhausted. If you have a State Pension or a defined-benefit pension, those pay in as taxed income from their own start ages and the net amount reduces how much needs to be drawn from everything else, rather than sitting in the pot order themselves. Pension withdrawals are grossed up for tax so the take-home amount actually covers what's needed, the same way a real UK pension drawdown works.
Does inflation affect the numbers I see?
Every figure you type in is in today's money, but the simulation itself runs in nominal, inflated pounds internally — because UK tax bands are frozen in nominal terms and a mortgage payment is a fixed nominal amount. The result is converted back to today's money before it's shown to you, so you never see a nominal number, but the maths underneath needed them to correctly capture fiscal drag.
Can I plan as a couple?
Yes — a toggle adds a second, independent salary and pension track, since UK income tax is assessed per person rather than jointly. Cash, ISA, LISA and GIA stay as one shared household pot, but salary, pension, and DB pension are tracked separately for each of you, because that's what actually determines whether one of you ends up paying higher-rate tax on drawdown while the other has unused headroom — and the calculator flags it when it spots a real imbalance.