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Coast FIRE calculator (UK)

Coast FIRE means you've already invested enough that compounding alone should carry it to your retirement target — no further contributions needed. From that point you only have to cover your current spending until retirement. Example: a £40,000/year retirement needs about £1.08M; at an illustrative 5% real growth you'd hit that at 57 from roughly £472,981 invested at age 40 — or from £665,531 if you're happy to work (but not save) until 50. The calculator works out your own number from your target, age and growth assumptions.

How the Coast FIRE number works

It's compound growth run backwards: Coast number = retirement target ÷ (1 + real growth)years to retirement. The further you are from retirement, the smaller the pot that can coast there. Two honest caveats: growth isn't guaranteed (a real-world plan should stress-test the assumption, not trust one rate), and the target itself should include UK tax on withdrawals — the £1.08M above does; a naive 25× doesn't quite.

Why Coast FIRE fits the UK system well

Coasting pairs naturally with the pension age lock: money already inside a SIPP at, say, 40 has to coast to 57 anyway — you couldn't spend it earlier if you wanted to. Many UK savers find their pension is already at or near its coast number, and the real remaining job is building the accessible (ISA/taxable) side: either to bridge an early retirement or simply to cover spending while the pension compounds. Checking the two sides separately — is the pension coasting? is the bridge funded? — tells you far more than one blended number.

Model your own numbers — ISA/SIPP split, the bridge to 57, Monte Carlo and more.

Open the free UK FIRE calculator →

Frequently asked questions

What is a Coast FIRE number?

The amount you need invested today so that growth alone reaches your retirement target by your chosen age, with no further contributions. It equals your target divided by (1 + real growth) to the power of the years remaining.

How much do I need to Coast FIRE at 40 in the UK?

For a £40,000/year retirement at 57 (target ≈ £1.08M), roughly £472,981 invested at age 40 at an illustrative 5% real growth. Your own figure depends on your target, timeline and growth assumption.

Does Coast FIRE include my pension?

It should — pension money is often the natural coasting pot, since it is locked until 57 anyway. Check the pension and your accessible savings separately: one may already be coasting while the other still needs building.

Coast, Lean & Barista FIREThe main flavours of FIRE for a UK audience — Coast, Lean, Barista, Fat and standard FIRE — what each means, the rough numbers, and which suits which situation. ISA vs pensionSaving for early retirement in the UK: pension gives tax relief but locks money until 57; ISA is tax-free and accessible any time. How much to retire?How much you need to retire in the UK, by target income — computed with UK tax on withdrawals.

InflectionFI is an educational planning tool, not financial or tax advice. Figures are estimates based on your inputs and stated assumptions. Verify your situation with a qualified adviser.