FIRE Calculator UK — Your Number, and the Bridge to 57

The short version. The standard FIRE number is your annual spending × 25, the same thing as a 4% withdrawal rate — £800,000 on £32,000 a year. That gets you a target. What it does not tell you is whether you can actually reach the money: in the UK a pension is locked until 55, and 57 from April 2028, so retiring earlier means funding the gap from ISAs and investments. WealthR works out the number, then tests it against the mix you actually hold. Free permanently.

The number, and why it is only the start

Annual spending multiplied by 25. That is it, and it is the same arithmetic as drawing 4% a year. Spend £32,000 and the number is £800,000; spend £45,000 and it is £1,125,000.

It is a good first number and a poor last one, for three British reasons. Your State Pension arrives partway through and changes what you need from your own money. Your wealth is split across wrappers with completely different access rules. And the tax on taking it out is not the same for every pound — a pension withdrawal is income, an ISA withdrawal is not.

The bridge: the part US guides cannot help with

Most FIRE writing is American, and the access rules there are different. In Britain the rule is simple and awkward: you cannot normally touch a pension until 55, and that becomes 57 on 6 April 2028.

So if the plan is to stop at 50, seven years have to come from money outside a pension. That stretch is the bridge, and it is where UK FIRE plans fail — not because the total was wrong, but because the money was in the wrong place at the wrong time. A £900,000 net worth that is 80% pension does not fund a 50-year-old.

ISAs do the bridging£20,000 a year, reachable at any age, and nothing to pay on the way out. That accessibility is exactly what the bridge needs, which is why ISA headroom matters more to an early retiree than to anyone else.
Pensions do the heavy lifting laterTax relief going in makes them the more efficient place to build — but locked until 55, soon 57. Efficient and unreachable at the same time.
The split is the real decisionNot "how much", but "how much, where". Two people with identical net worth can have very different earliest retirement dates purely because of the wrappers it sits in.
The State Pension lands last£241.30 a week, from 66 rising to 67. It cuts what you need from your own money in the late years and does nothing at all for the early ones.

WealthR models this month by month: what is drawn, which wrapper it comes from, what tax that costs, and whether the bridge holds all the way to the pension unlocking.

Is the 4% rule safe here?

It is a rule of thumb from American research into 30-year retirements, and a UK early retirement differs in ways that matter: a different tax system, the State Pension arriving partway through, and a longer run if you stop at 50 rather than 65.

So treat 4% as an illustration rather than a guarantee. WealthR uses it as the default and lets you move it between 2% and 7% — but the more useful answer comes from testing a plan against 5,000 simulated futures and reading how many of them survive. One projection gives one answer; the distribution tells you how much room for error you actually have.

The UK figures this runs on

2026/27 UK tax year. Scottish rates apply where your region is set to Scotland.
Figure	2026/27
Default withdrawal rate (adjustable 2–7%)	4%
Earliest a pension can normally be taken	55 → 57 from April 2028
ISA allowance (the bridge)	£20,000
Lifetime ISA (25% bonus, from 60 for retirement)	£4,000
Personal allowance	£12,570
England, Wales & N. Ireland bands	20% / 40% / 45%
Scottish bands (six)	19 / 20 / 21 / 42 / 45 / 48%
New State Pension	£241.30 a week

Coast, Barista and the rest

Coast FIREWhat you have already invested will reach your number by your target age with nothing more added. You keep working to cover living costs, but stop saving for retirement. It arrives years before full FIRE — there is a free calculator for it.
Barista FIREPart-time or lower-paid work covers part of your spending, so the pot only has to cover the rest. In the UK it also keeps National Insurance years accruing, which matters for the State Pension.
Lean and Fat FIREThe same arithmetic against a smaller or larger spending figure. Worth checking against what you actually spend rather than a round number.
Full FIREThe pot covers everything indefinitely. In Britain that still means clearing the bridge first.

What the free plan covers

Free, permanently, with no card

Your FIRE number from your own spending and withdrawal rate
The month-by-month forecast to 99, with the bridge years modelled explicitly
The chance your money lasts, from 5,000 simulated futures
The full UK tax engine across all four nations
Unlimited ISAs, SIPPs and pensions, plus property and physical assets
Household planning, so a couple can be modelled together or apart

WealthR Pro (£5.99 a month or £39.99 a year) adds the drawdown planner with withdrawal ordering, life-event scenarios and PDF reports. The number, the forecast and the simulation’s headline odds are not behind it.

Start with a calculator, or the whole picture

Questions people ask

How do I calculate my FIRE number in the UK?

The usual starting point is annual spending multiplied by 25, which is the same thing as a 4% withdrawal rate. On £32,000 a year that is £800,000. It is a useful first number and a poor last one, because in the UK part of your wealth sits in a pension you cannot touch yet, and the State Pension arrives later and changes what you need from your own money. WealthR works out the number and then tests it against your actual mix of ISAs, pensions and property.

What is the bridge in UK FIRE?

The years between stopping work and the age you can take a pension. A UK pension cannot normally be touched until 55, and that becomes 57 on 6 April 2028. So retiring at 50 means seven years funded entirely from money outside a pension — usually ISAs and general investments. It is the part of UK FIRE that American guides do not cover, because their rules are different, and it is where most UK plans fall over.

Is the 4% rule safe in the UK?

It is a rule of thumb from US research, not a law, and a UK retirement differs in ways that matter: different tax, the State Pension arriving partway through, and a longer run if you retire early. A 4% starting rate is a reasonable illustration and WealthR uses it as the default, adjustable between 2% and 7%. Testing it against 5,000 simulated futures tells you far more than the rate itself does.

Should I use an ISA or a pension for FIRE?

They do different jobs and this is not advice on which to choose. A pension gets tax relief going in and is taxed coming out, but is locked until 55, rising to 57. An ISA gets no relief, has a £20,000 annual limit, and can be reached at any age — which is what makes it the usual bridge. WealthR models whatever mix you actually hold and shows the tax each one costs when drawn, so the trade-off is visible in your own figures. For a decision about your own circumstances, speak to a regulated adviser.

What is Coast FIRE?

The point where what you have already invested will grow into your FIRE number by your target age without another penny going in. You still work and still cover your living costs, but you stop saving for retirement. It arrives years before full FIRE, which is why people find it motivating, and WealthR has a free calculator for it.

Does the State Pension count towards FIRE?

It does, but only from State Pension age — 66 and rising to 67 — so it reduces what you need from your own money in the later years rather than the early ones. At £241.30 a week in 2026/27 it is a substantial part of a modest retirement income. WealthR projects it from your National Insurance record and starts it on the right date rather than averaging it across the whole plan.

Find your number, then check the bridge holds

Your spending, your wrappers, your dates — with the years before 57 modelled explicitly. Free permanently, no card, no bank linking.

Work out your number free → Try the calculator first

WealthR is a planning and forecasting tool, not a financial adviser. WealthR Ltd is not authorised by the Financial Conduct Authority and nothing here is personal advice or a recommendation to buy, sell or hold anything, or to choose one tax wrapper over another. Projections are illustrations based on assumptions you choose, not predictions, and tax figures shown are for the 2026/27 UK tax year. For advice about your own circumstances, speak to a regulated adviser or MoneyHelper.