FIRE Number Calculator UK
Work out the pot you’d need to stop working — and the one number that decides how fast you get there: not your salary, but how much of it you save.
Your FIRE number — the goal at the heart of “Financial Independence, Retire Early” — is the size of pot that could fund your living costs indefinitely from its returns, so you no longer need to work. The classic rule of thumb is the 4% rule: multiply your annual spending by 25. Spend £30,000 a year and your FIRE number is £750,000; the idea is you can draw about 4% a year and the pot should last. Two things shift that figure more than people expect. First, your savings rate is the dominant lever — saving 50% of your income gets you to FIRE in roughly 17 years, while saving 10% takes over 50, because a higher savings rate both shrinks the target and grows the pot faster at the same time. Second, in the UK the State Pension changes the maths: once it starts (currently from age 66, rising to 67), the full new State Pension of around £12,548 a year covers part of your spending, so your private pot only needs to cover the gap from then on — though it must bridge the years before the State Pension kicks in. This calculator works out your FIRE number, how different withdrawal rates change it, and roughly how long it would take to reach. To project the growth, see the Compound Interest Calculator; for the tax wrappers, ISA vs SIPP vs GIA.
FIRE goal
Current investments
Monthly contributions
Growth and UK access assumptions
FIRE result
Your FIRE number
Calculating…
Calculating…
Time to FIRE
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Projected net worth
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Current progress
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Monthly needed
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ISA bridge status
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Coast FIRE number
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Your FIRE number — quick lookup
The left table shows the FIRE number for different levels of annual spending under the 4% rule (spending × 25). The right shows how the withdrawal rate you assume changes the target for the same £30,000 of spending. The core idea: your FIRE number is driven by what you spend, not what you earn — and by how cautious a withdrawal rate you choose.
| Annual spend | FIRE number |
|---|---|
| £20,000 | £500,000 |
| £30,000 | £750,000 |
| £40,000 | £1,000,000 |
| £50,000 | £1,250,000 |
| Withdrawal rate | Multiple | FIRE number |
|---|---|---|
| 3.0% | ×33 | £1,000,000 |
| 3.5% | ×29 | £857,000 |
| 4.0% | ×25 | £750,000 |
| 4.5% | ×22 | £667,000 |
Left: the FIRE number is your annual spending divided by your safe withdrawal rate; at 4% that’s spending × 25. Right: a more cautious withdrawal rate means a bigger pot — dropping from 4% to 3% raises the target for £30,000 of spending from £750,000 to £1,000,000. These are illustrative; the safe rate depends on your time horizon, investments, and assumptions, and real returns aren’t guaranteed.
How the FIRE number works
The FIRE number rests on a simple idea: if your pot is large enough that a sustainable yearly withdrawal covers your spending, you no longer depend on a salary. The maths is straightforward; the judgement is in the assumptions.
The 4% rule and the multiply-by-25 shortcut
The best-known guide is the 4% rule, drawn from US research suggesting that withdrawing 4% of a balanced portfolio in the first year, then rising with inflation, has historically lasted at least 30 years in most cases. Because 4% is one twenty-fifth, the shortcut is to multiply your annual spending by 25. Spend £30,000 a year and your FIRE number is £750,000. It’s a starting point, not a guarantee — it was based on a specific market history and a 30-year horizon, and early retirees planning for 40+ years often use a more cautious rate.
Why your savings rate is the real lever
The figure that decides how fast you reach FIRE isn’t your income — it’s the percentage of it you save. This is the central FIRE insight, and it works twice over. A higher savings rate means you spend less, which shrinks your FIRE number; and you invest more, which grows your pot faster. Saving 10% of your income takes over 50 years to reach independence; saving 25% takes around 32; saving 50% gets you there in roughly 17. The same salary, three completely different timelines, decided entirely by how much you keep. It’s why FIRE communities obsess over the savings rate above almost everything else.
Choosing a withdrawal rate
The 4% rule is a default, not a law. A more cautious 3.5% or 3% withdrawal rate suits longer retirements and gives more safety against poor early returns, at the cost of a larger pot. A higher 4.5% needs a smaller pot but carries more risk of running out. The right rate depends on how long your money must last, how your portfolio is invested, whether you’d cut spending in a downturn, and how much certainty you want. Early retirees planning for 40 or 50 years often lean toward 3–3.5%.
Worked examples
Four scenarios: a standard FIRE number, the savings-rate effect, the UK State Pension’s impact, and the lean-versus-fat FIRE spectrum.
Scenario 1 · A standard FIRE number
£30,000 a year needs £750,000
£30,000 × 25 = £750,000
Draw ~£30,000/year, rising with inflation
If you spend £30,000 a year, the 4% rule puts your FIRE number at £750,000. With a pot that size invested in a balanced portfolio, you could in principle draw around £30,000 in the first year and increase it with inflation each year, with a good historical chance of the money lasting a long retirement. It’s the figure that turns “retire early” from a vague wish into a concrete target you can plan and save toward — though it depends on assumptions that may not hold.
Scenario 2 · The savings-rate effect
10% vs 50% saved — 52 years or 17
Save 10% → spend £36k → target £900k → ~52 years
Save 50% → spend £20k → target £500k → ~17 years
This is the heart of FIRE. On the same £40,000 income, saving 10% means a 52-year journey, while saving 50% gets you to independence in about 17. The savings rate works on both ends: spending less shrinks the target (£500k versus £900k) and saving more fills the pot faster. This is why FIRE isn’t really about earning more — it’s about the gap between what you earn and what you spend. Widen that gap and the timeline collapses.
Scenario 3 · The UK State Pension
Your pot doesn’t have to cover everything
Before State Pension age: pot covers full £30,000
After: pot covers £17,452 → ~£436,000
The UK State Pension is a quiet advantage UK FIRE planners can factor in. Once it begins — currently age 66, rising to 67 — the full new State Pension of around £12,548 a year covers part of your spending, so your private pot only needs to fund the £17,452 gap from that point, a target of about £436,000 rather than £750,000. The catch: you must bridge the years before the State Pension starts, when your pot covers the full £30,000. Many UK plans size the pot for that bridge, knowing the requirement eases later.
Scenario 4 · Lean, regular, and fat FIRE
The same rule, three lifestyles
Regular FIRE (£30k/year): £750,000
Fat FIRE (£50k/year): £1,250,000
FIRE isn’t one-size-fits-all. “Lean FIRE” means living modestly — perhaps £20,000 a year — for a £500,000 target reachable far sooner. “Fat FIRE” funds a comfortable lifestyle of £50,000 or more, needing £1.25 million but no compromise on spending. Most people land somewhere between. Deciding which version you’re aiming for is the first step, because it sets the target — and your spending choices, more than your income, determine which is realistic for you.
Planning your FIRE number — four things UK savers should weigh
Most FIRE calculators just multiply spending by 25. But a realistic UK plan accounts for the State Pension, the tax wrappers, the risk of bad timing, and the lever that matters most. Work through these four:
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1
Have you maximised your savings rate?
This is the dominant lever. Because a higher savings rate both shrinks your target and grows your pot faster, it compounds twice — saving 50% reaches FIRE in ~17 years versus ~52 at 10%. Before fine-tuning withdrawal rates, focus on widening the gap between earning and spending.
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2
Have you factored in the State Pension?
From State Pension age, the full new State Pension (~£12,548/year) covers part of your spending, cutting the pot your investments must fund. But you need to bridge the years before it starts — so size your pot for the gap years, knowing the requirement eases once the State Pension and any private pensions begin.
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3
Are you using ISAs and pensions wisely?
UK FIRE leans on tax wrappers. A pension (SIPP) gives tax relief but is locked until the minimum pension age; an ISA is accessible any time, tax-free. Many use ISAs to bridge the early years and pensions for later. Where you hold the pot is as important as its size.
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4
Have you allowed for sequence risk?
A run of poor returns early in retirement can do lasting damage, because you’re withdrawing from a falling pot. This “sequence risk” is why a cautious withdrawal rate, a cash buffer, and flexibility to cut spending in a downturn matter. The 4% rule assumes you don’t panic-sell at the bottom.
£30,000/year spending — how the target shifts
Same spending, different assumptions:
The same £30,000 of spending can mean a target of £436,000 or £857,000 depending on the withdrawal rate you choose and whether you count the State Pension — which is why a single “spending × 25” figure is only the starting point. For UK savers the realistic process is: maximise your savings rate first, since it dominates everything; pick a withdrawal rate honest about your time horizon and nerve; factor in the State Pension and any workplace pensions for the later years while sizing the pot to bridge the gap before them; and use ISAs and pensions deliberately so the money is accessible when you need it. The 4% rule gives you a target; these adjustments make it a plan. The calculator lets you flex each assumption for your own numbers.
Coast FIRE — a gentler variant
Not everyone wants to retire as early as possible. Coast FIRE is the point where your existing pot, left to grow untouched, will reach your full FIRE number by traditional retirement age without any further contributions. Once you hit it, you no longer need to save for retirement — you only need to cover your current spending, freeing you to work less, switch to a lower-paid but enjoyable job, or stop overtime. It’s a popular middle path: you keep the security of a growing pot while regaining time and flexibility now, rather than grinding to a full FIRE number as fast as possible.
Two scenarios that change the picture
What if…
You cut your annual spending by £5,000?
What if…
Markets fall 30% in your first year retired?
Key FIRE terms explained
FIRE comes with its own vocabulary — withdrawal rates, lean and fat variants, coast and sequence risk. The ten below cover what you’ll meet planning your number.
- FIRE
- Financial Independence, Retire Early — building enough invested wealth that its returns cover your living costs, so paid work becomes optional rather than necessary.
- FIRE number
- The pot size you’re aiming for: your annual spending divided by your safe withdrawal rate. At 4%, that’s spending multiplied by 25.
- 4% rule
- A guide suggesting you can withdraw 4% of your pot in year one, rising with inflation, with a good historical chance of lasting 30 years. The basis for the ×25 shortcut.
- Safe withdrawal rate
- The percentage you draw each year that your pot can sustain. Lower rates (3–3.5%) suit longer retirements; higher rates need a smaller pot but carry more risk.
- Savings rate
- The share of income you save rather than spend. The dominant factor in how fast you reach FIRE, because it shrinks the target and grows the pot at once.
- Lean FIRE
- Reaching independence on a modest budget — perhaps £20,000 a year — for a smaller pot reachable sooner, at the cost of a tighter lifestyle.
- Fat FIRE
- Reaching independence with a comfortable budget — £50,000 a year or more — needing a much larger pot but no compromise on spending.
- Coast FIRE
- The point where your existing pot will grow to your FIRE number by traditional retirement age without further saving — so you only need to cover current spending.
- Sequence risk
- The danger that poor returns early in retirement do lasting damage, because you’re withdrawing from a falling pot. Why a cautious rate and a cash buffer matter.
- The bridge
- The years between retiring early and your pensions and State Pension starting, which your accessible savings (often ISAs) must fund in full.
Five mistakes people make with FIRE planning
FIRE is simple arithmetic but easy to plan badly. These five errors, drawn from the recurring r/FIREUK and r/UKPersonalFinance threads, are the common ones.
Focusing on income instead of savings rate
People assume a bigger salary is the route to FIRE, but the savings rate dominates the timeline. Saving 50% reaches independence in ~17 years versus ~52 at 10%, on the same income. Earning more only helps if you save the extra rather than spending it.
Cost: decades added to the journey Fix: maximise the gap between earning and spendingTreating the 4% rule as guaranteed
The 4% rule came from a specific US market history and a 30-year horizon. For a 40 or 50-year early retirement, a flat 4% may be too aggressive. Many use 3–3.5% for safety. Treat it as a starting estimate, not a promise that the money will last.
Cost: running out over a long retirement Fix: use a cautious rate for long horizonsIgnoring the bridge to pension age
Retiring at 45 means funding 20+ years before pensions and the State Pension start. People size a pot for their spending but forget the money must be accessible in those bridge years — pensions are locked until the minimum pension age, so ISAs usually fund the gap.
Cost: wealth you can’t access when you need it Fix: hold accessible (ISA) savings for the bridgeUnderestimating real spending
Basing the FIRE number on optimistic, stripped-back spending leaves no room for the real cost of living — irregular bills, healthcare, helping family, the occasional splurge. An undersized pot forces a return to work. Track actual spending for a year before setting the figure.
Cost: a pot too small for real life Fix: base it on tracked, realistic spendingForgetting sequence risk
A market crash in the first few years of retirement can do far more damage than the same crash later, because you’re selling units from a falling pot. Planning a flat 4% with no cash buffer or flexibility leaves you exposed. Build a buffer and be ready to trim spending in bad years.
Cost: lasting damage from bad early timing Fix: keep a cash buffer; stay flexible on spendingFrequently asked questions
What is a FIRE number?
Your FIRE number is the size of invested pot that could fund your living costs from its returns, so you no longer need to work for money. It’s calculated as your annual spending divided by your safe withdrawal rate.
At the common 4% rule, that’s your annual spending multiplied by 25 — so £30,000 a year of spending gives a FIRE number of £750,000. It’s the concrete target at the heart of Financial Independence, Retire Early planning.
How do I calculate my FIRE number?
Divide your expected annual spending in retirement by your safe withdrawal rate. At a 4% withdrawal rate, multiply your annual spending by 25; at a more cautious 3.5%, multiply by about 28.6.
So £30,000 of annual spending is £750,000 at 4%, or £857,000 at 3.5%. Base it on realistic spending — ideally tracked over a year — rather than an optimistic minimum, and consider reducing the figure for any State Pension or workplace pension you’ll receive later.
What is the 4% rule?
The 4% rule is a guideline suggesting you can withdraw 4% of your pot in the first year, then increase that amount with inflation each year, with a good historical chance of the money lasting at least 30 years.
It came from US research based on a specific market history and a 30-year retirement. For a longer early retirement of 40 or 50 years, many people use a more cautious 3% to 3.5%. It’s a useful starting point, not a guarantee — real returns vary and aren’t assured.
What’s the most important factor in reaching FIRE?
Your savings rate — the percentage of income you save rather than spend. It dominates the timeline because it works twice: spending less shrinks your FIRE number, and saving more grows your pot faster.
On the same income, saving 10% takes over 50 years to reach independence, 25% takes around 32, and 50% gets you there in roughly 17. This is why FIRE is less about earning a high salary and more about the gap between what you earn and what you spend.
Does the State Pension reduce my FIRE number?
Yes, for the years after it starts. Once you reach State Pension age (currently 66, rising to 67), the full new State Pension of around £12,548 a year covers part of your spending, so your private pot only needs to fund the remainder from that point.
For £30,000 of spending, that cuts the long-run target from £750,000 to around £436,000. But you must bridge the years before the State Pension starts, when your pot covers your full spending — so plans often size the pot for that earlier, heavier period.
What’s the difference between Lean, Fat, and Coast FIRE?
Lean FIRE means reaching independence on a modest budget (perhaps £20,000 a year), for a smaller pot reachable sooner. Fat FIRE funds a comfortable lifestyle (£50,000+), needing a much larger pot.
Coast FIRE is different: it’s the point where your existing pot, left to grow untouched, will reach your full FIRE number by traditional retirement age — so you stop saving for retirement and only need to cover current spending, freeing you to work less now.
How should I hold my FIRE pot in the UK?
UK FIRE planning leans heavily on tax wrappers. A pension (such as a SIPP) gives tax relief on contributions but is locked until the minimum pension age; an ISA is accessible at any time, with tax-free growth and withdrawals.
Many people use ISAs to fund the early “bridge” years of an early retirement, since the money is accessible, and pensions for the later years once they can be drawn. Where you hold the pot is as important as its total size. See ISA vs SIPP vs GIA for the trade-offs.
What is sequence risk?
Sequence risk is the danger that poor investment returns early in retirement do lasting damage. Because you’re withdrawing money while the pot is down, you sell more units at low prices, leaving less to recover when markets rise.
The same crash later in retirement matters far less. It’s why a cautious withdrawal rate, a cash buffer to avoid selling at the bottom, and the flexibility to trim spending in bad years are important — the 4% rule assumes you don’t panic-sell during a downturn.
Related calculators
A FIRE plan connects to growing the pot, the tax wrappers, and the everyday saving that funds it. These calculators handle each piece.
Methodology & sources
How the maths works
The calculator works out your FIRE number as your expected annual spending divided by your chosen safe withdrawal rate. At the commonly cited 4% rate this equals annual spending multiplied by 25; at 3.5% it’s about 28.6 times, and at 3% about 33 times. To estimate the time to reach the target, it compounds your current pot and annual contributions at an assumed real (after-inflation) return until the balance reaches your FIRE number. For the UK State Pension adjustment, it reduces the spending your private pot must cover from State Pension age by the full new State Pension amount, while noting that the pot must cover full spending in the bridge years before the State Pension and any private pensions begin. The Lean, Regular, and Fat FIRE figures simply apply the same rule to different spending levels.
These are illustrative estimates to help you set a target, not personal advice, a forecast, or a guarantee. The 4% rule is based on historical US market data over a 30-year horizon and may not hold for longer early retirements, different markets, or future conditions; investment values can fall as well as rise, and a poor sequence of early returns can shorten how long a pot lasts. The State Pension amount, age, tax rules, and ISA and pension allowances are set by government and change over time. Your own safe withdrawal rate depends on your investments, time horizon, and flexibility. The aim is to help you understand and estimate your FIRE number, not to recommend that you retire early or follow any particular strategy.
Assumptions and conventions used
- FIRE number = annual spending ÷ safe withdrawal rate
- 4% rule → spending × 25 (the default shortcut)
- Cautious rates: 3.5% ≈ ×28.6, 3% ≈ ×33
- Time to FIRE compounds pot + contributions at a real return
- State Pension (full new ~£12,548/yr) reduces post-SP-age need
- The bridge: pot covers full spending before pensions start
- Savings rate is the dominant lever on the timeline
- Lean/Regular/Fat FIRE = the same rule at different spending
- Figures shown are illustrative, not predictions