What Is a FIRE Number?
Updated June 2026 · 6 min read · Free calculator inside
✓ Checked against the 4% rule methodology
FIRE stands for Financial Independence, Retire Early. Your "FIRE number" is the size of investment pot that could fund your lifestyle indefinitely from returns and withdrawals, so that paid work becomes optional. Here is how it is estimated.
Work out your FIRE number and target age
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Open the FIRE Calculator →The 25x rule
A common starting point is 25 times your annual spending. If you need £30,000 a year, your FIRE number is about £750,000. The logic comes from the 4% safe withdrawal rate, since 1 ÷ 0.04 = 25.
The 4% rule
The 4% rule suggests that withdrawing about 4% of your pot in the first year of retirement, then adjusting for inflation, has historically had a high chance of lasting 30+ years. It is a guide, not a guarantee — some choose a more cautious 3–3.5%.
Worked example
- Annual spending: £40,000.
- FIRE number at 25x: £1,000,000.
- A more cautious 30x (3.3% withdrawal): £1,200,000.
Variations of FIRE
- Lean FIRE — a smaller pot funding a frugal lifestyle.
- Fat FIRE — a larger pot for a more comfortable lifestyle.
- Coast FIRE — investing enough early that growth alone reaches your number by retirement age.
Frequently Asked Questions
How do I calculate my FIRE number?
Multiply your expected annual spending in retirement by 25 (the inverse of the 4% rule). For £30,000 a year that is £750,000.
Is the 4% rule safe?
It has historically worked for 30-year retirements in most scenarios, but it is not guaranteed. Longer retirements or poor early returns may call for a lower withdrawal rate such as 3–3.5%.
Does my pension count towards FIRE?
Yes. Pensions, ISAs and other investments all count toward your FIRE number, though access ages differ — private pensions are usually locked until your late 50s.
Work out your FIRE number and target age
Skip the maths — get an instant, up-to-date figure with our free calculator.
Open the FIRE Calculator →Related Guides
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⚠️ Disclaimer: This guide is for general information only and does not constitute financial, tax, or legal advice. Rates and thresholds can change — always check the latest figures on GOV.UK and consult a qualified professional before making decisions.