Most people think of FIRE as a single moment — the day your portfolio is large enough to live off forever. But there's a much earlier, more reachable milestone that almost every UK investor will hit before full FIRE: Coast FIRE. It's the point where you've front-loaded enough money into your portfolio that you no longer need to add anything — compound growth on its own carries you to a full FIRE number by your target retirement age. Your job income only has to cover your living costs from now until retirement. The retirement saving is done.
It matters because it's a permission slip. Hit Coast FIRE in your 30s and you can switch to a lower-paid job you actually like, drop to four days a week, take a sabbatical, start a business — all without ever touching your existing pot, and still arrive at full retirement on schedule. That's a fundamentally different kind of freedom from waiting decades for full FIRE.
The formula
Coast FIRE is built from three numbers: your full FIRE number, your real return assumption, and the years until you retire.
And the FIRE number itself is just:
So if you want £35,000/year in retirement and your full FIRE number is £875,000, and you're 32 with a target retirement age of 60 at 5% real return, your Coast FIRE number is £875,000 ÷ (1.05)28 ≈ £224,000. Hit £224,000 today and you can stop contributing, and the pot will grow to £875,000 by age 60. That's the entire game.
Coast FIRE is in real terms — read this carefully
The single biggest mistake in DIY Coast FIRE calculators is mixing real and nominal numbers. A 7% nominal return at 3% inflation is only a 4% real return — so if you use a 7% return alongside today's spending number, you'll dramatically understate the pot you need, because you've forgotten that future spending will be inflated too.
The fix is to work in real terms throughout: real return, real spending, real pot. The calculator above does this — when it says you need £224,000, that's £224,000 in today's purchasing power. Whatever the nominal pound figure ends up being in 2050, it'll buy you the same as £224,000 buys today.
The UK pension access cliff
Coast FIRE works the same way mathematically in any country, but UK investors have a wrinkle US calculators ignore: SIPPs and workplace pensions can normally be accessed from age 55, rising to 57 from 6 April 2028. Anyone retiring after that date meets the 57 rule, which is the age used in the example below.
This matters if your target retirement age is below 57. Say you want to retire at 50 with a £35,000/year lifestyle. Your full FIRE number is still ~£875,000 — but if all £875,000 is inside a SIPP, you can't touch any of it for seven years. You need a bridge fund in ISAs or other accessible accounts to cover from 50 to 57. That's typically £35,000 × 7 ≈ £245,000 in ISAs minimum.
The split, in practice, looks like:
- Retiring at 57 or later: the whole pot, pension included, is accessible from the start. Pension contributions get tax relief at your marginal rate and grow free of tax.
- Retiring at 50–56: the bridge years are paid from outside the pension. Roughly: bridge years × annual spend held in ISAs or other accessible accounts.
- Retiring before 50: the bridge runs longer than the years spent drawing on the pension, so a single-pot Coast FIRE figure hides more of the picture; a multi-pot model shows the two pots separately.
The full WealthR app sizes the bridge pot: how much needs to sit in accessible accounts (ISA, GIA) to cover the years before your pension can be accessed, set against what you hold there now.
What withdrawal rate to use in the UK
The famous 4% rule (the Trinity Study) was built on US data — mostly US large-cap equities and US Treasury bonds, over 1926–1995. It's a useful starting point but probably optimistic for a UK investor today because:
- UK long-term equity returns have been lower than US.
- 30+ year retirements (think early FIRE) are longer than the 30-year horizon in the original Trinity Study.
- Sequence-of-returns risk (a market crash in your first few years) is more punishing the longer you have to fund.
The current consensus among UK FIRE planners is somewhere in the 3.25%–3.5% range for high confidence. A 3.5% rate needs a pot 14% larger than the 4% rule does, and in exchange leaves more margin against a poor run of returns.
Should you actually stop contributing once you hit Coast FIRE?
On the calculator's assumptions, yes — that's the definition. What carrying on contributing changes:
- Margin against returns being lower than assumed. If 5% real becomes 3% real, your Coast FIRE pot won't quite get there.
- Retirement age. Further saving can bring retirement earlier than the target.
- Employer pension contributions. In many workplace schemes the employer's contribution stops when yours does.
The dividend allowance is one of the figures named in the speculation ahead of the Autumn Budget on 28 October 2026, so it is worth knowing where it stands when you plan around it.
What moves the Coast FIRE date
- When contributions go in. Money paid in earlier has longer to compound. Early on, growth is small relative to contributions; the balance shifts as the pot grows.
- Tax on growth. Growth inside ISAs and pensions is not taxed; outside them, dividend and capital gains tax reduce what compounds.
- Employer pension contributions. A matched contribution adds 50–100% to the amount you pay in.
- Fees. A 1% fee gap compounds to ~25% of your final pot over 30 years.