Rule of 25 Calculator (FIRE)

25x is the exact inverse of the 4% safe withdrawal rate from the Trinity Study. If your portfolio is 25 times what you spend each year, withdrawing 4% in year one covers a full year of expenses. The math is symmetric: target = expenses / (rate / 100), and 1 / 0.04 = 25. Drop the rate to 3.5% and the multiplier rises to about 28.6x. Push it to 5% and it falls to 20x. The calculator solves both directions for you.

Lean FIRE is a stripped-down retirement on roughly $25,000 to $40,000 a year, which lands at a 15x to 20x multiplier when paired with a higher withdrawal rate or a paid-off house. Regular FIRE covers a normal middle-class budget of $50,000 to $80,000 and uses the classic 25x figure. Fat FIRE targets $100,000 a year or more with a 33x to 40x cushion (a 2.5% to 3% withdrawal rate) so the portfolio can carry travel, healthcare, and a much longer retirement horizon. Pick the rate that matches the lifestyle you actually want to fund.

Your FIRE number is denominated in today's dollars, so the projection has to be too. A 7% nominal return with 3% inflation is only a 4% real return: that is the rate at which your purchasing power actually grows. Project at nominal 7% and you will hit your target on paper years before your money can actually buy the lifestyle you planned for. The inflation-adjustment checkbox subtracts the inflation rate from your expected return so the projected years to FIRE reflect real spending power, not just bigger numbers on a brokerage statement.

A bad market in your first five retirement years can permanently shrink the portfolio, even when long-term average returns are fine. Selling shares at depressed prices to fund withdrawals locks in losses that future gains cannot fully recover. The 4% rule already bakes in some of this risk through its Monte Carlo backtests, but practitioners often hold 1 to 2 years of expenses in cash, run a bond tent that overweights bonds at retirement and shifts back to stocks later, or use a flexible withdrawal strategy that trims spending by 10% to 15% in down years to keep the portfolio intact.

For a 30-year retirement using a 50/50 to 75/25 stock/bond mix, the original Trinity Study (Cooley, Hubbard, Walz, 1998) and its updates report success rates of 95% or higher across every rolling 30-year period since 1926. Bengen's original 1994 paper found the same. For 40 to 50-year horizons typical of early retirees, researchers such as Wade Pfau and the Early Retirement Now safe withdrawal series suggest stepping down to 3.3% to 3.5% to keep similar safety margins, which corresponds to a 28x to 30x multiplier. This is an estimate, not personalized financial advice.