What is Coast FIRE?
In short: you have saved enough that your existing investments, untouched, will grow into a complete retirement fund by the age you mean to stop working. From that day you still earn — but only to pay this month's bills. The saving race is over, which is why coasters so often downshift into work they actually like. The flagship Coast FIRE Calculator explains the mechanics in full, and the FIRE glossary covers every term of art.
This British edition runs the same honest, real-return arithmetic against the system you actually save through: ISAs you can raid at any age, pensions locked until your mid-fifties, and a State Pension that eventually carries part of the load. Enter four numbers, get one verdict — coasting, on track, or behind — plus the exact monthly contribution that repairs a Behind result.
Where ISAs, SIPPs and the LISA fit
Britain hands you two fundamentally different vehicles. An ISA is flexible forever: £20,000 a year in allowance, tax-free growth, and withdrawals at any age with no tax consequences whatsoever. A SIPP (or workplace pension) is generous but patient money — tax relief at your marginal rate now, in exchange for being locked until age 55, rising to 57 from 2028. For a coasting plan that asymmetry is the whole design problem: coasting is precisely about gaining the freedom to stop saving early, and locked pension money cannot buy freedom before it unlocks.
Hence the ISA bridge: enough pension contributions to capture any employer match, everything else into ISAs, with the ISA pot sized to carry spending from your retirement date to pension access. The LISA earns its place in the name as a niche middle path — it draws on your overall ISA allowance rather than adding to it, and carries its own age and access rules — but for most UK coasters the working split is simply ISA-first, SIPP-second. Inside this calculator the distinction shows up in one place: the retirement tax-rate slider, where ISA-heavy plans justify a lower rate than fully-drawn pensions.
The State Pension: enter it in Advanced
Open Advanced settings and enter the annual amount you expect plus the age it starts. The engine then builds a two-phase plan — a bridge fund carrying spending from your retirement until the State Pension begins, then a smaller portfolio requirement once it flows. For scale: the full new State Pension is roughly £12,000 a year, though your actual entitlement depends on your National Insurance record — check your State Pension forecast on gov.uk rather than assuming the maximum. The qualifying age is currently 66 and rises to 67 by 2028, so enter the start age that genuinely matches your plan; a later start means the bridge phase has more years to fund alone.
A worked example
Oliver is 32 with £80,000 invested across ISAs and a workplace pension. He spends £2,800 a month, adds £600 a month, and targets retirement at 67, assuming a 6% nominal return against 2.5% inflation. These are this page's defaults, so what loads in the calculator is his situation exactly.
- FIRE number: £33,600 of annual spending ÷ a 4% withdrawal rate = £840,000 at age 67.
- Coast number at 32: £259,364. Oliver sits at about 31%, so the verdict reads Behind.
- The solver's fix: £127/month more closes the gap by 67.
Behind is not a judgement, it is a quotation: at his current pace the plan falls short, by an amount expressible as £127 a month. That is the entire value of a verdict-first calculator — the difference between vague anxiety about retirement and a number small enough to act on this payday. Flip the crash test afterwards to check whether the plan survives markets dropping 30% tomorrow.
Frequently asked questions
ISA or SIPP — where should my coast money go?
For a coasting plan, ISAs usually come first. Your £20,000 annual allowance grows free of tax and stays accessible at any age, which is vital if you want the option to stop saving years before pension access arrives. A SIPP, or workplace pension, wins on tax relief at your marginal rate — but the money is locked until 55, rising to 57 from 2028, so it cannot fund an early bridge. A common pattern: contribute enough to the pension to capture any employer matching, then send everything else to the ISA that becomes your pre-pension bridge and your proof that you are genuinely coasting. This calculator does not care where the assets sit; enter the total invested and use the retirement tax-rate slider to reflect how much will be taxed on the way out.
How does the State Pension change my coast number?
Enter it in Advanced settings as an annual amount with its start age, and the engine splits your plan in two: a bridge fund carrying spending from retirement until the State Pension begins, then a much smaller nest egg for afterwards, when that income covers part of the budget. The full new State Pension is roughly £12,000 a year — check your State Pension forecast on gov.uk for your actual entitlement — so it covers a meaningful share of a modest retirement budget and shrinks both the FIRE number and today's coast number accordingly. The claim age matters as much as the amount: it is currently 66 and rises to 67 by 2028, and could move again before you claim. The later the start age you enter, the bigger the bridge has to be.
Can I retire before I can touch my SIPP?
That is precisely what the ISA bridge is for. Pension funds stay locked until age 55 — 57 from 2028 — so any plan that stops work earlier needs accessible money to live on until the unlock date. Build that bridge inside ISAs: withdrawals are tax-free at any age, with no income-tax consequences and no forced ordering. In this calculator, model it by entering your total invested assets and your actual target retirement age, then sanity-check separately that the money you will spend before pension access fits comfortably inside your ISA holdings rather than your SIPP. Retiring at 50 with a pension-heavy portfolio reads better on paper than it lives. The verdict tells you whether compounding finishes the job; the bridge is what carries you to the first cheque.
What return and inflation should I assume for a UK portfolio?
The page opens with a 6% nominal return against 2.5% inflation — a sober planning pair for a globally diversified, low-cost portfolio measured in pounds. Converted properly, (1 + nominal) ÷ (1 + inflation) − 1, that works out near 3.4% real, and every output here is shown in today's money rather than inflated future figures. Both numbers sit under Advanced settings, and nudging them is the cheapest honesty test available: drop the return to 5% or lift inflation to 3% and watch how much later your coast point arrives. UK investors are often tempted to assume home-market portfolios beat global ones — history offers weak support for that, and these defaults deliberately assume nothing clever. Boring global index funds plus correct real-return maths is the entire method.
Is a 4% withdrawal rate safe in the UK?
The 4% rule was built on US market history, and UK researchers have long argued a slightly lower starting rate fits British returns better — sequencing risk does not respect borders, and neither do decades of mediocre local performance. The practical approach: leave SWR at 4% for your first pass through this calculator, then drag the safe-withdrawal slider down to 3.5% and see what it costs in extra years of work or extra monthly saving. If your plan still holds at 3.5%, you have built in a margin most UK retirees never check. Remember the rate only sets your FIRE number — annual spending divided by SWR — so lowering it raises both the retirement target and today's coast number together. Better to learn that from a slider than from reality.
Wherever you are between paydays, the arithmetic stays the same. For the full formula treatment, the flagship calculator owns it; if part-time work sounds better than full coasting, the Barista FIRE Calculator sizes the income that bridges you; and when the verdict reads Behind, stress-test the withdrawal rate behind your target or see how many working days stand between you and retirement. Know your number first; everything else is negotiation with yourself.