How to use this UK Coast FIRE calculator
- Enter your age, the age you want to stop work completely, and what you hold in ISAs and in pension pots today.
- Enter what you pay into each every month until you coast. For pensions, include your employer's contribution and tax relief, because that is what actually lands in the pot.
- Enter your yearly spending in retirement in today's pounds, and check the pension access age and State Pension details.
- Read your Coast FIRE number, what each pot needs, the age you get there and how the plan holds up in the risk tests.
How is Coast FIRE calculated in the UK?
Your Coast FIRE number is your retirement target discounted back to today at your expected real (after-inflation) return:
Coast FIRE number = FIRE number at retirement ÷ (1 + real return)years until retirement
The FIRE number is the pot that can fund your spending for the rest of your life. Without other income that is 25 times your spending at a 4% withdrawal rate, the shortcut popularised by the FIRE movement[1] and based on William Bengen's research[2]. In the UK the State Pension covers part of your spending from State Pension age, so the calculator values each retirement year separately and you need less.
UK savers also need a second number. Pensions can't normally be drawn before the minimum pension age, 57 from 6 April 2028[10], while ISA money can be taken out at any time[11]. If you plan to stop work before your pension opens, part of your Coast FIRE number has to be in ISAs, enough to grow into the spending for those early years. If you stop at or after your pension access age, there is no ISA requirement at all.
Worked example: Sam, 30
Sam wants to stop work at 60 and spend £28,000 a year, and expects the full new State Pension, about £12,548 a year, from 68. With 7% returns, 3% inflation and 0.1% fees, the real return is 3.79%.
- FIRE number at 60, after the State Pension: £479,639
- Coast FIRE number at 30: £479,639 ÷ 3.05 = £157,290
- Because 60 is after the pension access age, all of it can be in pensions.
Sam has £20,000 in ISAs and £40,000 in a workplace pension, and pays in £400 a month to ISAs and £500 to the pension. At that rate Sam reaches Coast FIRE at 42, with about £254,026 saved. From then on Sam could stop saving for retirement and only earn enough to cover the bills.
How does Coast FIRE work if you stop before your pension age?
Bring Sam's retirement forward to 55 and two things change. The target rises to £526,148, because the money has to last five years longer, and £55,268 of it must be in ISAs to pay for ages 55 and 56. Discounted to today, Sam needs £207,776 in total and at least £21,826 of it in ISAs. Saving as before, Sam coasts at 50 instead of 42.
The calculator checks both parts. If your pots are big enough in total but too much is in your pension, it tells you so and shows how much your ISAs are short. Shifting some monthly saving from pension to ISA fixes that, but costs you tax relief, so the cheapest fix is often to move retirement closer to 57. A Lifetime ISA doesn't help with this gap: money taken out before 60 for anything other than a first home loses 25%[18].
How much does the State Pension lower your Coast FIRE number?
A lot, because it is a large, inflation-protected income for life. The full new State Pension is £241.30 a week in 2026/27[3], and it rises each year by the highest of earnings growth, CPI inflation or 2.5%[4]. In Sam's example, leaving it out raises the Coast FIRE number from £157,290 to £229,553. Counting only half of it gives £193,421.
The age matters too. State Pension age rises from 66 to 67 between 2026 and 2028 and is due to reach 68 between 2044 and 2046[6]; for anyone born on or after 6 April 1978 it is 68 under current law[7]. A third review began in July 2025 and had not reported when we last checked[8]. If Sam's State Pension started at 67 rather than 68, the Coast FIRE number would be £153,740, a difference of£3,549. Use your own State Pension age from your forecast.
Coasting has one advantage over full early retirement here. You keep working, so you can keep building National Insurance qualifying years. You need 35 for the full new State Pension[4] and 10 for any at all[5]. Your State Pension forecast shows how many you have and what you are on track for[9]; enter that amount rather than the full rate if it is lower.
How much do you need to coast at each age?
The earlier you reach it, the less you need, because the money has longer to compound. For £25,000 a year of spending, a full State Pension from 68, a 4% withdrawal rate and a 3.79% real return:
| Your age now | Retire at 55 (of which ISAs) | Retire at 60 | Retire at 65 |
|---|---|---|---|
| 25 | £147,947 (£16,182) | £110,192 | £78,801 |
| 30 | £178,159 (£19,487) | £132,695 | £94,893 |
| 35 | £214,541 (£23,467) | £159,792 | £114,271 |
| 40 | £258,352 (£28,259) | £192,423 | £137,607 |
Retiring at 60 or 65 needs no ISA money because the pension is already open. Retiring at 55 needs some of the total in ISAs, shown in brackets, to cover the two years before 57.
Where should you keep saving before you coast?
The faster you reach your Coast FIRE number, the sooner you can ease off, so tax efficiency matters. Pension contributions get tax relief on up to 100% of your earnings; with relief at source your provider adds basic rate relief of 20% to your pot[14]. The annual allowance is £60,000 a year, and unused allowance may be carried forward from the previous three tax years[15]. ISAs take up to £20,000 a year in 2026/27[16], and from 6 April 2027 no more than £12,000 of that can go into cash ISAs if you are under 65[17]. For a long coasting period, stocks and shares ISAs are the usual home for the bridge.
When you finally retire, you can usually take up to 25% of each pension tax-free, up to a lifetime total of £268,275[12]. The rest of your pension and the State Pension are taxed as income once your total income is above your Personal Allowance, usually £12,570[13]. Include that tax in the spending you enter.
What return should a UK coaster assume?
Coast FIRE leans on compounding over decades, so the return assumption drives the answer. Over 1900-2008, UK shares returned 5.09% a year after inflation and US shares 6.01%[19]. If you knock that 0.92 percentage point gap off Sam's 3.79% real return, the Coast FIRE number for retiring at 60 rises from £157,290 to £205,450.
The calculator works in today's pounds, so inflation only matters through the real return. The Bank of England's target is 2%[23], and UK CPI was 3.5% in the 12 months to September 2026[24]. The default of 3% sits between them. On withdrawal rates, the highest rate that survived every 30-year UK retirement from 1900 was 3.77%[19], and longer early retirements point to 3.25%-3.5%[20]. Lowering the withdrawal rate raises your Coast FIRE number in proportion.
What if markets fall after you start coasting?
That is the main risk of Coast FIRE. Once you stop paying in, you no longer buy cheaply after a crash, and the returns in your first decade of retirement largely decide how much you can safely spend[22]. The risk section replays your plan through 2,000 simulated market histories and every retirement start year since 1928. Those tests use US data from 1928 to 2025[21], which has been stronger than UK history, so a UK investor should read the success rates as a best case and prefer the "Match my return" setting. The methodology page explains how both tests work, and our guide to what Coast FIRE is covers the idea in more depth.
If the success rate is lower than you would like, keep a small monthly contribution going after you hit the number, coast a few years later, or plan some part-time work before full retirement. The UK FIRE calculator shows how much earlier you could stop work altogether if you keep saving at your current rate.
How does Coast FIRE work for couples in the UK?
Enter combined ISAs, combined pensions and combined retirement spending, and use the age of the partner who will stop work last. Each partner has their own ISA allowance, pension annual allowance and State Pension, so add both State Pension forecasts together. If one of you has a final salary pension, add it in the calculator with its own start age.