FIRE Calculator — Financial Independence, Retire Early
Find your FIRE number, the age you hit it, and how far along you already are — then drag the sliders to see how savings rate and spending change the date.
After inflation — long-run equities are often assumed at ~5%
The classic '4% rule'
Net worth by age
| Age | Net worth | Progress to FIRE |
|---|---|---|
| 31 | £81,409 | 10.9% |
| 32 | £103,888 | 13.9% |
| 33 | £127,491 | 17.0% |
| 34 | £152,275 | 20.3% |
| 35 | £178,298 | 23.8% |
| 36 | £205,621 | 27.4% |
| 37 | £234,311 | 31.2% |
| 38 | £264,436 | 35.3% |
| 39 | £296,066 | 39.5% |
| 40 | £329,278 | 43.9% |
The maths of FIRE
Financial independence arrives when your portfolio can fund your spending indefinitely: FIRE number = annual expenses ÷ withdrawal rate. At the classic 4% rate that's 25× expenses; at a more conservative 3.5% it's about 28.6×. The projection then compounds your savings monthly at your assumed real return until net worth crosses the line.
Worked example
Age 30 with £60,000 invested, spending £30,000 a year, saving £1,500 a month at 5% real returns: the FIRE number is £750,000, reached in 19 years and 9 months — financial independence at age 50.
Frequently asked questions
What is a FIRE number and how is it calculated?
Your FIRE number is the portfolio size that can sustainably fund your spending: annual expenses ÷ withdrawal rate. Spending £30,000 a year at a 4% withdrawal rate means a FIRE number of £750,000 — i.e. 25× annual expenses.
What is the 4% rule?
A rule of thumb from the Trinity study: withdrawing 4% of a diversified portfolio in year one, then adjusting for inflation, historically survived 30-year retirements in the vast majority of scenarios. Early retirees with longer horizons often plan on 3–3.5% to be safer.
Why do my expenses matter more than my income?
Spending counts twice: every pound of annual spending adds 25 pounds to your FIRE number (at 4%), and money not spent can be saved instead. Cutting £200 a month of permanent spending shrinks the target by £60,000 and raises your savings rate at the same time.
Should I use real or nominal returns?
This calculator expects a real (after-inflation) return, so the FIRE number stays in today's money. Long-run global equity returns after inflation have historically been roughly 5%; using nominal returns here would make the date look unrealistically close.