FIRE (Financial Independence, Retire Early) Calculator
Calculate your (Financial Independence, Retire Early) number and how long until financial independence.
What this calculator does
This FIRE calculator models a single ISA or general investment pot rather than a pension, because pension drawdown conventions do not apply to money you manage yourself. It runs two phases: contributions compound at your expected return until your desired retirement age, then contributions stop and withdrawals begin at your chosen spend level, rising each year with inflation.
Simulating the drawdown rather than stopping at a target is what makes it useful. It reports not only when you first reach a number but whether the pot survives to 95, and if it does not, the age it runs dry. That depletion age is usually the more important of the two figures.
When to use it
Reach for it when you are comparing lifestyles rather than pursuing a single number. Switching between Lean, Traditional, Fat, Barista and Coast reruns the whole simulation at that spend level, which shows how many extra working years separate a frugal exit from a comfortable one.
It is also the natural tool for the bridging problem UK early retirees face. If you stop at 50 but cannot touch a pension until 57, the ISA has to carry seven years alone. Model that by setting the retirement age you want, then adding your expected tax-free lump sum at your access age to see the pot step back up.
Understanding the inputs
Current savings means money you can reach at any age, so stocks and shares ISAs and general investment accounts, not pension pots. Expenses drive four of the five FIRE types, so enter genuine annual or monthly spending rather than income. Barista part-time income should be net of tax, since it offsets spending the portfolio would otherwise fund.
Pension access age is used only by Coast FIRE; set it to 57 unless you reach 55 before April 2028. Expected return and inflation jointly determine the real return that discounts every target, so the gap between them matters far more than either figure alone. Deduct platform and fund charges from your return before entering it.
How is this calculated?
Each FIRE target is the present value of that lifestyle's annual spend, drawn every year of retirement and rising with inflation, discounted at your expected real return (your return net of inflation) — not a flat 4% rule, which is a pension drawdown convention that doesn't apply to a self-managed ISA/brokerage pot. The projection itself accumulates until your desired retirement age, then switches to withdrawing that spend level (inflation-adjusted) from your actual balance, so you can see whether the money really lasts.
A worked example
Take a 35-year-old with £80,000 in an ISA, adding £1,500 a month at 6 percent with 2.5 percent inflation, spending £40,000 a year, aiming to stop at 55. The pot reaches roughly £958,000 by 55. The Traditional target, being the present value of £40,000 a year to 95 at a 3.4 percent real return, is about £866,000, so the plan clears.
Fat FIRE at £52,000 a year needs roughly £1,125,000, which this pot misses, and the drawdown runs the balance to zero at about age 86. Coast is nowhere near: £80,000 growing untouched to 57 reaches only around £288,000 against a target near £844,000.
Limitations and assumptions
These are projections under fixed assumptions, not predictions. A single flat annual return with no volatility cannot express sequence-of-returns risk, which is the biggest threat to a long early retirement. Two pots with the same average return can end very differently depending only on when the poor years happen to land.
The model also assumes withdrawals are tax-free, ignores capital gains tax outside an ISA and the £20,000 annual subscription limit, holds spending and contributions flat, fixes the horizon at 95, and excludes the State Pension entirely. Read the depletion age as a warning about your assumptions rather than a date in your diary.
Common Questions
- Why is there no 4 percent rule here?
- The 4 percent rule is a pension drawdown convention designed around a 30-year retirement, and it does not transfer to a self-managed ISA pot funding forty or more years. This calculator instead prices each target as the present value of a level real spend running to age 95, discounted at your own real return.
- Is this modelling a pension or an ISA?
- An ISA or general investment account: a single pot you can draw from at any age. Pensions enter only through the pension access age used by Coast FIRE, and an optional tax-free lump sum you can inject at a chosen age. That is why the withdrawal phase can start well before 55.
- When can I access my pension, and does it matter here?
- Normally 55, rising to 57 from April 2028. It matters for Coast FIRE, which asks whether today's balance grows into a Traditional FIRE number by that age without further contributions. It also defines the bridging period your ISA has to cover if you stop working in your forties or early fifties.
- What do the five FIRE types cover?
- Lean funds 70 percent of your current expenses, Traditional 100 percent, and Fat 130 percent. Barista funds your expenses less the part-time income you expect to keep earning. Coast assumes you stop contributing today and rely on growth alone to reach Traditional FIRE by your pension access age.
- Does choosing a type change more than the target?
- Yes. The selected type drives the entire simulation, not just the number displayed. Picking Fat FIRE makes the withdrawal phase draw 130 percent of your expenses every year, rising with inflation, so each type has its own accumulation path, its own drawdown, and its own verdict on whether the pot lasts.
- What does the depletion warning mean?
- It means the simulation carried your balance through the withdrawal phase and it reached zero before 95. Hitting a target number is not the same as the plan working, because withdrawals rise with inflation while the assumed return stays flat. A depletion age tells you to contribute more, spend less, or step down a FIRE type.
- How should I use the tax-free lump sum field?
- It models a one-off injection into the pot at a specific age, most obviously the 25 percent tax-free element of a defined contribution pension taken at your access age. That element is capped by the lump sum allowance of £268,275. Enter the amount and the age, and the chart shows the step up.
- How much can I put into an ISA each year?
- The ISA allowance is £20,000 per tax year across all ISA types, which works out at roughly £1,666 a month. If your monthly contribution above exceeds that, the surplus has to go into a general investment account, where dividends and capital gains are taxable and annual exemptions are now small.
- Why does it assume age 95?
- Because planning to average life expectancy leaves around half of people short, and an early retiree has a very long horizon. Ninety-five is a deliberately cautious assumption that makes targets look large, which is the point. It is a fixed constant in this calculator rather than something you can change.
- What return and inflation figures are sensible?
- Around 5 to 7 percent nominal for a global equity tracker after platform and fund charges, with inflation at 2.5 percent. The gap between them is your real return, and that is what discounts every target. Dropping real return from 3.5 percent to 2.5 percent raises a Traditional FIRE target substantially, so test both.