- Your FIRE number is roughly 25× your annual spending — the basis of the "4% rule."
- Coast FIRE means your current savings alone, with no further contributions, would reach your FIRE number by a normal retirement age.
- Years to FIRE depends heavily on your savings rate, not just your income.
- Hunch tracks net worth and savings rate over time so you always know your real distance to FI.
How the FIRE calculator works
Enter your annual spending, current savings, and monthly contribution. The calculator computes your FIRE number (25× spending), projects how long it takes to reach it at your current savings rate, and finds your Coast FIRE crossover — the point at which you could stop contributing entirely and still reach FI by a standard retirement age.
The math: the 4% rule and Coast FIRE
FIRE number = annual spending × 25, derived from the 4% rule (a 4% annual withdrawal rate is widely considered sustainable over a ~30-year retirement). Years to FIRE compounds your current savings forward with contributions at an assumed return until the balance reaches your FIRE number. Coast FIRE crossover finds the earliest point at which your current balance alone, compounding with zero further contributions, would still reach the FIRE number by your target retirement age.
Worked example
Spending $48,000/year gives a FIRE number of $1,200,000. Starting from $80,000 with $2,000/month contributions at a 7% return reaches that number in about 19 years. The same $80,000 starting balance, left alone with no further contributions, would reach Coast FIRE for a 65 retirement in just a few years — after which further contributions just shorten the full-FIRE timeline rather than being strictly required.
Key terms
- FIRE number
- The invested net worth needed to sustain your spending indefinitely — typically 25× annual spending.
- 4% rule
- A guideline that a portfolio can sustain a 4% annual withdrawal rate (inflation-adjusted) without running out over roughly 30 years.
- Coast FIRE
- The point at which current savings, left to grow with no further contributions, would reach your FIRE number by a standard retirement age.
- Lean / Fat FIRE
- Variants of FIRE based on spending level — Lean FIRE targets a minimal-spending FIRE number, Fat FIRE targets a higher-spending, more comfortable one.