# My FIRE Number: FIRE formulas and reference figures, one per line
# Source: our own method, explained at https://myfirenumber.app/how-we-calculate/ (checked 2026-10-12). Returns are real (after inflation) and are assumptions; this is arithmetic, not advice.
# Format: kind | name | rule and example | page
Formula | FIRE number | yearly spending ÷ withdrawal rate; at 4% that is 25 × spending, at 3.5% about 28.6 ×, at 3% about 33.3 × | https://myfirenumber.app/fire-number/
Example | FIRE number at 4% | $50,000 a year ÷ 0.04 = $1,250,000 | https://myfirenumber.app/fire-number/
Formula | Growth with yearly saving | balance next year = balance × (1 + real return) + yearly saving, applied once a year with the saving added at the end of the year | https://myfirenumber.app/
Example | Years to FIRE | $150,000 invested, $24,000 saved a year, 5% real: $1,250,000 is reached in 21 years | https://myfirenumber.app/
Formula | Coast FIRE number | FIRE number ÷ (1 + real return)^(years until retirement): the amount that grows to the FIRE number with nothing more added | https://myfirenumber.app/coast-fire-calculator/
Example | Coast FIRE at 32 for 60 | $1,250,000 ÷ 1.05^28 = $318,867 | https://myfirenumber.app/coast-fire-calculator/
Formula | Barista FIRE number | (yearly spending − part-time earnings after tax) ÷ withdrawal rate | https://myfirenumber.app/barista-fire-calculator/
Example | Barista FIRE | ($50,000 − $20,000) ÷ 0.04 = $750,000, against $1,250,000 for full FIRE | https://myfirenumber.app/barista-fire-calculator/
Formula | Needed with a pension | (yearly spending − pension or Social Security) ÷ withdrawal rate, in today’s money; × (1 + inflation)^years for the retirement year’s money | https://myfirenumber.app/how-much-do-i-need-to-retire/
Formula | Yearly saving to hit a target by a date | (target − balance × (1 + r)^n) × r ÷ ((1 + r)^n − 1) for n years at real return r; (target − balance) ÷ n when r is 0 | https://myfirenumber.app/early-retirement-calculator/
Formula | Years to FI from a savings rate | with savings rate s, real return r and withdrawal rate w, starting from zero: ln(1 + (1 − s) × r ÷ (s × w)) ÷ ln(1 + r); (1 − s) ÷ (s × w) when r is 0 | https://myfirenumber.app/financial-independence-calculator/
Example | Savings rate 10% | 51.4 years to FI at 5% real and a 4% withdrawal rate | https://myfirenumber.app/financial-independence-calculator/
Example | Savings rate 25% | 31.9 years to FI at 5% real and a 4% withdrawal rate | https://myfirenumber.app/financial-independence-calculator/
Example | Savings rate 50% | 16.6 years to FI at 5% real and a 4% withdrawal rate | https://myfirenumber.app/financial-independence-calculator/
Example | Savings rate 75% | 7.1 years to FI at 5% real and a 4% withdrawal rate | https://myfirenumber.app/financial-independence-calculator/
Formula | Years the money lasts | portfolio P paying W a year (rising with inflation) at real return r: forever if W ≤ P × r, else ln(W ÷ (W − P × r)) ÷ ln(1 + r); P ÷ W when r is 0 | https://myfirenumber.app/safe-withdrawal-rate-calculator/
Example | 5% withdrawal at 3% real | $1,000,000 paying $50,000 a year at 3% real lasts about 31 years | https://myfirenumber.app/safe-withdrawal-rate-calculator/
Formula | 4 percent rule | first-year withdrawal = 4% of the portfolio, then the same dollar amount rising with inflation each year; $1,000,000 gives $40,000 in year one | https://myfirenumber.app/4-percent-rule-calculator/
Reference | Bengen 1994 | William Bengen, Journal of Financial Planning, October 1994: with 50% stocks and 50% intermediate-term government bonds, rebalanced yearly, 4% never exhausted the portfolio in under 33 years for any start year from 1926, while 4.25% could fail in 28; the 4.15% worst-case figure he named SAFEMAX comes from his later work (2006, for an October 1968 retiree) | https://myfirenumber.app/4-percent-rule-calculator/
Reference | Trinity study 1998 | Cooley, Hubbard and Walz, AAII Journal, February 1998: 4% inflation-adjusted withdrawals from a 50/50 stock and corporate bond portfolio succeeded in 95% of 30-year periods between 1926 and 1995; taxes and fees were not included | https://myfirenumber.app/4-percent-rule-calculator/
Reference | Why early retirees use less | the 4% rule was tested over 30 years; a 40- to 60-year retirement has more chances to hit a bad run, so planning figures of 3.25% to 3.5% are common | https://myfirenumber.app/safe-withdrawal-rate-calculator/
Formula | Real return | (1 + nominal return) ÷ (1 + inflation) − 1; 7.5% nominal with 2.5% inflation is about 4.9% real | https://myfirenumber.app/