Nominal value · dotted line = FIRE number · shaded band = Lean → Fat FIRE range
Sensitivity: Years to FIRE at Different Returns
Annual Return
FIRE Number
Years to FIRE
Pot at Target Age
Shortfall / Surplus
Sensitivity: How Spending Changes Your FIRE Number
Annual Spend
FIRE Number
Years to FIRE
Coast FIREIf you stop contributing today and just let compound growth do the work, you need £– invested right now to coast to your FIRE number by your target retirement age.
4% Safe Withdrawal Rate — what it means
Trinity University research found that a portfolio withdrawing 4% annually had a very high historical survival rate over 30-year retirements using US stock/bond data. For UK FIRE with longer retirements, many use 3–3.5%. Adjust the SWR above to model your preference.
What is FIRE and how do I calculate my number?
FIRE (Financial Independence, Retire Early) is a movement focused on aggressive saving and investing to reach financial independence far earlier than the traditional retirement age. Your FIRE number is the size of investment portfolio that generates enough passive income to cover your annual expenses indefinitely.
The most common formula: FIRE Number = Annual Spending ÷ Safe Withdrawal Rate (SWR). At the widely-used 4% SWR, you need 25× your annual expenses. At 3.5% SWR you need 28.6×. Lean FIRE targets 75% of your planned spend; Fat FIRE targets 150%.
Coast FIRE is the amount you need invested today that will grow to your FIRE number by your target age, without any further contributions. Once you hit your Coast FIRE number, you only need to cover your living expenses — the market does the rest.
For UK FIRE discussion, see r/FIREUK. Always consider pension access age (currently 57 from 2028), ISA allowances, and the impact of inflation on your withdrawal purchasing power.