Quick answer: Your FIRE number is 25× your annual expenses (the 4% rule). If you spend £30,000/year you need £750,000. Use the calculator below to find your number and how many years it'll take at your savings rate.
Your FIRE number
£625,000
Years to FIRE
18
What is FIRE?
FIRE — Financial Independence, Retire Early — means saving enough that your investments can fund your lifestyle indefinitely. The target is 25× your annual expenses, based on the 4% safe withdrawal rule.
The FIRE tiers
| Tier | Annual spend | FIRE number |
|---|---|---|
| Lean FIRE | ~£16,000 | £400,000 |
| Regular FIRE | £25,000–£35,000 | £625,000–£875,000 |
| Fat FIRE | £50,000+ | £1.25m+ |
The UK FIRE strategy
Use pensions for the tax relief (especially higher-rate) but remember they lock until 55/57 — so use ISAs (£20k/year, accessible any time) to fund the "bridge years" before pension age. Always take the full employer pension match first.
Sequence-of-returns risk
A market crash in your first decade of withdrawals can derail FIRE. Mitigate with 1–3 years of cash, a slightly lower withdrawal rate (3.5%), and flexibility to cut spending in down years.
Frequently asked questions
FIRE stands for Financial Independence, Retire Early. The goal is to save and invest aggressively so that your portfolio can fund your lifestyle indefinitely, typically using the 4% safe withdrawal rule.
Your FIRE number is 25× your annual expenses (based on the 4% rule). If you spend £30,000/year, your FIRE number is £750,000. Some people use 28× or 33× for more conservative planning.
Yes, but it requires a high savings rate (often 50%+). UK pensions offer strong tax relief which accelerates the journey, though early withdrawal restrictions (55 now, 57 from 2028) mean you'll typically use ISAs for the gap years before pension age.
Lean FIRE covers essentials only (~£20k/year for a UK single). Regular FIRE supports a moderate lifestyle (£30-40k). Fat FIRE targets higher spending (£60k+). Each has its own FIRE number.
For UK FIRE, a mix is usually best. Pensions give 20-45% tax relief but lock funds until 55/57. ISAs are tax-free and accessible any time. A common strategy: fill pension for employer match and higher-rate relief, then use ISAs for the pre-pension bridge.
The 4% rule is based on US historical data. UK sequence-of-returns risk, inflation, and longer retirement horizons mean some planners use 3.5% as safer. Your adviser can run cash-flow modelling for your specific situation.