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Free UK investing tool
FIRE Calculator: Work Out Your FIRE Number and Retirement Age
Enter your savings, monthly contributions and target retirement spending to see the portfolio you need for financial independence, how many years it takes to get there, and the age you could stop working.
Last updated: July 2026. Figures shown in today's money, adjusted for inflation.
The short answer
Your FIRE number is the size of the investment portfolio you need before you can live off it. It is calculated by dividing your target annual spending by your safe withdrawal rate.
FIRE number = annual spending ÷ safe withdrawal rateIf you expect to spend £30,000 a year and use a 4% withdrawal rate, your FIRE number is £750,000. At a more cautious 3.5% rate, it rises to roughly £857,000. The calculator below works out how long it takes you to get there.
Calculate your FIRE number
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What is FIRE?
FIRE stands for Financial Independence, Retire Early. It is an approach to money where you save and invest a large share of your income so that, at some point well before the state pension age, your portfolio can pay for your living costs without you needing to work.
The mechanics are straightforward, even if the discipline is not. You keep your spending well below your income, invest the difference in low-cost funds, and let compounding do the heavy lifting. Once your portfolio is large enough that a sustainable withdrawal covers your annual costs, you are financially independent. Whether you then actually retire is a separate decision, and plenty of people in the FIRE community carry on working in some form.
Key point
Financial independence is a portfolio size, not an age. Two people the same age with the same salary can reach it decades apart purely because of the gap between what they earn and what they spend.
How your FIRE number is calculated
Your FIRE number is your target annual spending divided by your safe withdrawal rate. The withdrawal rate is expressed as a decimal, so 4% becomes 0.04 and 3.5% becomes 0.035.
Worked example: if you want £40,000 a year and use a 4% withdrawal rate, you divide 40,000 by 0.04 to get £1,000,000. Drop the withdrawal rate to 3.5% and the same £40,000 of spending now needs roughly £1,143,000, an increase of about 14%.
That sensitivity is the single most important thing to understand about FIRE maths. Small changes to your withdrawal assumption move your target by a lot, and so do small changes to your spending. Cutting £200 a month from your budget reduces a 4% FIRE number by £60,000.
Common FIRE numbers at a 4% withdrawal rate
| Annual spending | At 4% | At 3.5% | At 3% |
|---|---|---|---|
| £20,000 | £500,000 | £571,000 | £667,000 |
| £30,000 | £750,000 | £857,000 | £1,000,000 |
| £40,000 | £1,000,000 | £1,143,000 | £1,333,000 |
| £50,000 | £1,250,000 | £1,429,000 | £1,667,000 |
| £60,000 | £1,500,000 | £1,714,000 | £2,000,000 |
| £75,000 | £1,875,000 | £2,143,000 | £2,500,000 |
Figures rounded to the nearest £1,000. These are portfolio targets in today's money, before any tax you may owe on withdrawals outside an ISA.
How to use this FIRE calculator
Each input changes the result in a specific way. Here is what the calculator is asking for and what a sensible starting figure looks like for a UK investor.
| Input | What it means |
|---|---|
| Current age | Used to work out the age you reach your target. Nothing else depends on it. |
| Current invested savings | Everything already working for you: Stocks and Shares ISA, workplace pension, SIPP, general investment account. Exclude your home and your emergency fund. |
| Monthly contribution | Your total monthly investing, including employer pension contributions, since those grow in the same portfolio. |
| Annual spending in retirement | Your future budget in today's money. Many people find this is lower than their current spending once commuting, childcare and pension contributions drop away. |
| Expected annual return | The nominal return before inflation. A globally diversified equity portfolio has historically delivered somewhere around 7% to 9% before inflation, but with very large swings along the way. |
| Expected inflation | The Bank of England has a 2% CPI target. Using 2.5% builds in a small buffer. |
| Safe withdrawal rate | How much of the portfolio you draw in year one. Lower is safer and slower. |
| Annual contribution increase | How fast your investing grows each year. Setting this equal to inflation keeps your contributions flat in real terms. |
The calculator converts your return and your contribution growth into real terms by subtracting inflation, then projects the portfolio month by month. That is why every figure on screen is stated in today's money: a £750,000 target in 2046 buys what £750,000 buys now, not what it would nominally be worth then.
The 4% rule, and why early retirees often use less
The 4% rule comes from the Trinity Study, US research that looked at historical stock and bond returns and asked how much a retiree could withdraw each year, rising with inflation, without running out of money. It found that a 4% initial withdrawal from a portfolio with a substantial equity allocation survived almost every historical 30 year window.
The catch for the FIRE crowd is the number 30. If you stop working at 40, your portfolio may need to last 50 years or more, and the safety margin that works over three decades is thinner over five.
Reasons to be more cautious than 4%
- Longer retirements. A 50 year withdrawal period has meaningfully worse historical outcomes than a 30 year one.
- UK returns have differed from US returns. The original research is built on US market history, which has been unusually strong. UK and global portfolios have not always matched it.
- Fees eat into the rate. A 0.5% a year platform and fund cost is effectively half a percent off your withdrawal rate.
- Sequence of returns risk. A poor first few years of retirement does far more damage than the same poor years later on, because you are selling units while prices are low.
Reasons 4% may be conservative in practice
- Most people are flexible. Trimming spending in a bad year dramatically improves the odds, and almost nobody withdraws mechanically regardless of what markets do.
- The State Pension arrives later. For most UK early retirees, state pension income eventually reduces the amount the portfolio has to cover.
- Historical worst cases are rare. In most historical periods a 4% withdrawal left the retiree with more money than they started with.
The calculator defaults to 3.5% because that is the range most UK early retirees settle on. You can set it anywhere between 1% and 10% to see how much the target moves.
Types of FIRE explained
FIRE is not one target. The community has split it into variants that describe different spending levels and different degrees of "retired".
| Type | What it means | Rough UK portfolio |
|---|---|---|
| Lean FIRE | Financial independence on a deliberately small budget, usually under £25,000 a year for a single person. Fast to reach, but leaves little slack. | £500,000 to £700,000 |
| Regular FIRE | Independence on a comfortable middle-income budget, roughly £25,000 to £60,000 a year. | £700,000 to £1.7m |
| Fat FIRE | Independence without cutting back, typically £60,000 a year or more. Needs a large portfolio or a high income. | £1.7m and above |
| Coast FIRE | You have invested enough that compounding alone will reach your FIRE number by a normal retirement age. You still work, but you no longer need to save. | Varies by age |
| Barista FIRE | Part-time or lower-stress work covers some of your spending, so the portfolio only has to cover the rest. | Reduced target |
Portfolio ranges assume a withdrawal rate between 3.5% and 4%. They are illustrative rather than definitive, and your own number depends entirely on your spending.
What Coast FIRE means on this calculator
The Coast FIRE figure in the results shows how much you would need invested today for growth alone, with no further contributions, to reach your FIRE number by age 65. If your current portfolio is already above that figure, you have technically hit Coast FIRE: you could stop investing entirely and still arrive at a normal retirement age with enough.
FIRE in the UK: ISAs, SIPPs and the pension bridge
Most FIRE content is written for a US audience, and the account rules do not transfer. Two things matter a great deal for UK investors, and neither shows up in a generic calculator.
Where you hold the money changes the outcome
- Stocks and Shares ISA. You can pay in up to £20,000 across all ISAs in the 2026/27 tax year, under HMRC's ISA rules. Growth and withdrawals are free of UK income tax and capital gains tax, and you can access the money at any age. This makes an ISA the natural home for the years between early retirement and pension age.
- SIPP or workplace pension. Contributions attract tax relief at your marginal rate, which is a very large head start, especially for higher and additional rate taxpayers. The trade-off is that you cannot touch it until the normal minimum pension age.
- Lifetime ISA. Up to £4,000 a year, counting towards the £20,000 ISA allowance, with a 25% government bonus. It sits awkwardly with FIRE because penalty-free withdrawals for retirement do not start until 60.
- General investment account. No allowance limit, but gains and dividends are taxable. Usually the overflow once the ISA is full.
The overall ISA allowance is £20,000 for 2026/27. From 6 April 2027 the amount that can go into a Cash ISA falls to £12,000 a year for those under 65, though the total allowance across all ISA types stays at £20,000. Confirmed in the GOV.UK ISA reform factsheet.
The pension bridge problem
The normal minimum pension age, the earliest most people can access a private pension or SIPP, is 55, and it rises to 57 on 6 April 2028. The State Pension age is 66 and is rising to 67 between 2026 and 2028.
If you plan to stop working at 45, that leaves roughly twelve years before you can touch pension money and over twenty before any State Pension arrives. The portfolio that funds those years has to sit outside a pension. In practice that means a Stocks and Shares ISA, topped up by a general investment account once the ISA allowance runs out.
Planning note
A common UK approach is to split contributions: enough into a pension to capture employer matching and higher-rate tax relief, and the rest into an ISA to build the bridge. Our calculator projects your total portfolio, so if your FIRE age lands before 57 it will flag that part of the pot needs to be accessible.
How to reach FIRE faster
Four levers move your FIRE date, and they are not equally powerful. Ranked roughly by impact:
- Raise the gap between income and spending. Your savings rate is by far the strongest lever, because it cuts the target and grows the portfolio at the same time. Going from saving 20% of your income to 40% typically takes more than a decade off the timeline.
- Attack the three big costs. Housing, transport and food usually account for most of a UK household budget. A single decision on where you live outweighs years of small economies.
- Raise your income. A pay rise only helps if it does not become spending. Directing raises straight into investments is what turns career progress into early retirement.
- Cut investment costs. Platform fees, fund charges and FX costs come straight out of your compounding. On a £500,000 portfolio, a 0.5% difference is £2,500 a year. Our UK broker fees calculator shows what different platforms would cost you.
Two things that matter less than people expect: picking individual winning stocks, and timing your entry into the market. Both add risk without reliably shortening the timeline.
What this calculator does not include
Being clear about the limits matters more in retirement planning than in most other maths. This tool makes several deliberate simplifications.
- It assumes a steady return. Real markets do not deliver 7% every year; they deliver 25% one year and minus 18% the next. Smooth averages understate the risk of retiring just before a downturn.
- It ignores tax on withdrawals. ISA withdrawals are tax free, but income drawn from a SIPP above your personal allowance is taxable, and gains in a general investment account may be too.
- It excludes the State Pension. Adding it would lower the portfolio you need from your State Pension age onwards, so most people's true requirement is slightly lower than the figure shown.
- It assumes constant spending. Real retirement spending tends to fall in later years, apart from care costs.
- It excludes fees. To account for costs, subtract your total platform and fund charges from the expected return input.
Treat the output as a planning target and a way to compare scenarios, not as a promise about a specific date.
Frequently asked questions
What is a good FIRE number in the UK?
There is no universal figure, because it depends entirely on your spending. A single person spending £25,000 a year needs roughly £625,000 at a 4% withdrawal rate, while a couple spending £45,000 needs about £1.1m. The useful exercise is to work out your real annual spending first, then divide by your chosen withdrawal rate.
Can I retire early at 40 in the UK?
Yes, but it requires a high savings rate and careful account planning. The bigger obstacle is usually not the total portfolio but where it sits: you cannot access a private pension until 55, rising to 57 in April 2028, and the State Pension not until 66 or 67. Retiring at 40 means funding roughly seventeen years from ISAs and taxable accounts before pension money becomes available.
Is the 4% rule reliable for UK investors?
It is a reasonable starting point rather than a guarantee. The research behind it used US market history and a 30 year retirement. UK investors retiring very early face a longer withdrawal period and a different market history, which is why many use 3% to 3.5% instead. Being willing to reduce spending in poor years improves the odds more than any adjustment to the starting rate.
Should I use an ISA or a SIPP for FIRE?
Most UK FIRE plans use both. A pension gives you tax relief on the way in, which is a significant boost, particularly for higher rate taxpayers, but the money is locked until at least 55, rising to 57 from April 2028. An ISA has no tax relief on contributions but is completely accessible, which is what funds the years between early retirement and pension age. A common approach is to secure employer matching and higher-rate relief in the pension, then direct the rest into a Stocks and Shares ISA.
How much do I need to invest each month to retire early?
Run the numbers above with your own figures, since the answer swings on your target spending. As a rough illustration: starting from zero at 30, with a 5% real return and a £750,000 target, you would need to invest roughly £1,600 a month to get there by 50, or about £950 a month to get there by 55.
What is Coast FIRE and how is it different?
Coast FIRE is the point where your existing investments, left alone, will grow into your full FIRE number by a normal retirement age. You still need income to cover current living costs, but you no longer need to save for retirement. It usually arrives many years before full FIRE and gives people the freedom to move to lower-paid or lower-stress work.
Does this calculator account for inflation?
Yes. It converts your expected return and contribution growth into real terms by removing your inflation assumption, then reports every figure in today's money. A £750,000 result means a portfolio with the same buying power as £750,000 has now, not a nominal balance decades from now.
Do I need to include my house in my FIRE number?
No. Your home is not producing income you can withdraw, so it should not count towards the portfolio. It does affect the other side of the equation though: owning outright by the time you retire cuts your annual spending substantially, and a lower spending figure lowers your FIRE number.
Related calculators and next steps
FIRE planning touches several parts of your finances. These free tools cover the rest:
- Compound interest calculator: see how a lump sum and regular contributions grow over any period.
- UK broker fees calculator: compare what different UK platforms would charge on your portfolio.
- Find your broker: answer a few questions and get matched to a platform that fits how you invest.
Choosing where to invest
Platform and fund costs come directly out of your compounding, so the account you pick affects your FIRE date. Answer five questions to see which UK platforms fit your plan.
Or read our reviews of platforms often used for long-term investing:
This calculator is an educational illustration, not personal financial advice. It assumes a steady annual return, while real investment returns rise and fall, so treat every figure as a planning guide rather than a forecast. The value of investments can go down as well as up and you may get back less than you put in. Tax treatment depends on your individual circumstances and may change. If you are unsure, speak to an FCA-regulated financial adviser.
