How to use this UK FIRE calculator
- Enter your age, take-home pay (after tax, National Insurance and any pension deductions) and what you spend. The difference is treated as money going into ISAs.
- Enter what goes into your pensions each year, counting your employer's contribution and tax relief, and the balances in your ISAs and pension pots today.
- Check your pension access age and State Pension details. Add a final salary pension if you have one.
- Read your FI age, the ISA vs pension split, the what-if table and the risk tests.
Choose "A couple" to plan as a household. Every result updates as you type, and the share link saves your scenario.
How much do you need to retire early in the UK?
Your FIRE number is the total you need invested on the day you stop work. Without other income it is simply yearly spending ÷ safe withdrawal rate: 25 times spending at the classic 4% rate, which comes from William Bengen's 1994 study of US market history[18]. The State Pension and any final salary pension lower that number, but only from the age they start, so the calculator values every retirement year's spending separately and adds the years up.
Worked example: Priya, 32
Priya takes home £42,000, spends £28,000 and puts the other £14,000 into a stocks and shares ISA. With her employer's contribution and tax relief, £8,000 a year goes into her workplace pension. She has £30,000 in ISAs and £45,000 in her pension, and expects the full new State Pension from 68. With 7% returns, 3% inflation and 0.1% fees her real return is 3.79%.
- She can retire at 48, when her pots reach about £575,766.
- Of that, at least £223,075 must be in ISAs to cover the 9 years until her pension opens at 57. By 48 her ISAs should hold £354,741, so the bridge is covered.
- The remaining £352,691 can sit in her pension, which should hold £253,197 by then.
Without the State Pension, Priya would need £700,000 to retire at 48, and at her saving rate she would get there at 51 instead.
Why do ISAs and pensions need different amounts?
Because they unlock at different ages. You can take money out of an ISA at any time without losing any tax benefits[15]. A workplace pension or SIPP can't normally be touched before the normal minimum pension age, which rises from 55 to 57 on 6 April 2028[1]. So if you retire at 50, seven years of spending have to come from ISAs, cash or a general investment account, however big your pension is.
The calculator therefore tests two things each year: whether your ISAs and pensions together reach the total you need, and whether your ISAs alone cover the years before your pension opens. You can retire in the first year both are true. The ISA "bridge" is valued the same way as the rest of the plan, at the rate implied by your withdrawal rate, so the two parts add up exactly to the total.
Here is how the split moves with retirement age for Priya's £28,000 budget, with a full State Pension from 68 and a pension access age of 57:
| Retire at | Total needed | Must be in ISAs | Can be in pensions |
|---|---|---|---|
| 45 | £592,379 | £282,408 | £309,971 |
| 50 | £563,249 | £179,375 | £383,873 |
| 55 | £526,148 | £55,268 | £470,880 |
| 57 | £508,733 | None | £508,733 |
| 60 | £479,639 | None | £479,639 |
Retiring later lowers the total, because the money has fewer years to last and the State Pension covers a larger share of them. It shrinks the ISA requirement much faster: from 57 on, everything can come from pensions.
The bridge can delay you even when the total is there. If Priya sent most of her savings to her pension instead (£4,000 a year into ISAs and £18,000 into her pension), her two pots would reach the total at 48, but her ISAs couldn't cover the years to 57 until she was 51. The calculator flags this case and shows how many years the locked pension is costing you.
When can you take money from your pension?
From 6 April 2028 the normal minimum pension age is 57; until then it is 55. Some people keep a protected pension age, and members of the firefighters', police and armed forces schemes are exempt from the rise[1]. If you are 56 or older today you will already be 57 by April 2028, so the change mostly affects anyone younger, which is why the calculator defaults to 57 for most ages.
Once your pension opens, you can usually take up to 25% of it tax-free. The total tax-free cash across all your pensions is capped by the lump sum allowance at £268,275, and the lifetime allowance no longer exists[10]. The rest is taxed as income, and so is the State Pension. You pay Income Tax when your total income is above your Personal Allowance, usually £12,570[11]. The full new State Pension alone comes to £12,547.60 a year, just £22.40 under that allowance, so after State Pension age most pension withdrawals are taxable. Build that tax into your retirement spending.
How does the State Pension change your FIRE number?
The full new State Pension is £241.30 a week in the 2026/27 tax year, up from £230.25 in 2025/26[2]. That is £12,547.60 over 52 weeks, which the calculator rounds to £12,548. Each year it rises by the highest of earnings growth, CPI inflation or 2.5%[3], so treating it as a constant amount in today's pounds is a reasonable, slightly cautious assumption.
When it starts matters as much as how much it is. State Pension age is rising from 66 to 67 between 2026 and 2028 and is due to reach 68 between 2044 and 2046[5]. Anyone born on or after 6 April 1978 has a State Pension age of 68 under current law[6], which covers most people planning FIRE today. A third review of State Pension age started in July 2025 and had not reported when we last checked[7], so it is worth testing a later age.
How much you get depends on your National Insurance record. You need 35 qualifying years for the full new State Pension[3] and at least 10 to get any[4]. Someone who starts work at 22 and retires at 45 may have only 23 qualifying years, so early retirees often have gaps. Voluntary Class 3 contributions cost £18.40 a week in 2026/27[8], about £956.80 for a full year. Your official forecast shows your record, any gaps and whether paying to fill them would raise your State Pension[9].
ISA or pension: where should your FIRE savings go?
Usually both. Pensions win on tax: contributions get tax relief up to 100% of your earnings, and with relief at source your provider adds basic rate relief of 20%, so £200 from your pay becomes £250 in your pot[12]. Employer contributions only go into the pension. The limit is the annual allowance of £60,000 a year, lower if your income is very high, and you may be able to carry forward unused allowance from the previous three tax years[13].
ISAs win on flexibility. You can pay in up to £20,000 in the 2026/27 tax year[14], and from 6 April 2027 no more than £12,000 of that can go into cash ISAs if you are under 65[16]. A Lifetime ISA adds a 25% bonus on up to £4,000 a year, but money taken out before 60 for anything other than a first home loses 25%[17], so it works more like a pension for early retirement.
A sensible order for most early retirers is to take any employer match first, then build enough in ISAs to cover the bridge, then use the pension for the rest. In Priya's case, putting an extra £250 a month into either pot moves her FI age from 48 to 47; the what-if table in the calculator runs the same test on your numbers. Because pension money comes with tax relief, the same take-home cost buys a bigger pension contribution.
What withdrawal rate should you use in the UK?
The 4% rule was built on US data, and the US has been one of the best-performing markets. Using Dimson, Marsh and Staunton's data for 1900-2008, UK shares returned 5.09% a year after inflation against 6.01% for US shares, and the highest withdrawal rate that lasted through every 30-year UK retirement was 3.77%, compared with 4.02% in the US[19].
Early retirement also lasts longer than 30 years. For 50 to 60 year retirements, research on US data points to 3.25%-3.5%[20]. At 3.5%, Priya would need £636,429 and could retire at 49 rather than 48. Use the "Use a 3.5% withdrawal rate" row of the what-if table to see the cost in years for your plan.
Does the risk test use UK market data?
No, and it is important to know that. The Monte Carlo simulation and the historical backtest replay US share, US Treasury and US inflation data from 1928 to 2025[21]. UK markets have historically returned less than US markets[19], so the "Raw history" results are likely to flatter a UK or global portfolio. Switch the risk test to "Match my return" to keep the pattern of booms and crashes but scale it to your own expected return. The methodology page explains both tests.
The tests matter because the order of returns matters: a bad decade early in retirement does far more damage than the same decade later[22]. For inflation, the Bank of England targets 2%[23], while UK CPI was 3.5% in the 12 months to September 2026[24]. The default of 3% sits between the two; because results are in today's pounds, inflation only matters through the real return.
How does UK FIRE work for couples?
Couples have two of almost everything that matters here: two ISA allowances (£40,000 a year between you), two pension annual allowances, two Personal Allowances and two State Pensions, each based on its own National Insurance record. Choose "A couple", enter combined pay, spending and pots, use the younger partner's age (the longer, safer horizon), and add both State Pensions together. If your State Pension ages differ by more than a year or two, enter the later one, or add one partner's State Pension as the final salary pension with its own start age. The UK Coast FIRE calculator shows when you could stop saving and let your pots grow on their own.