FIRE Early Retirement Calculator
Calculates how many years until you reach financial independence and can retire early using the FIRE framework. Use it to test the impact of your annual savings, spending level, and chosen FIRE target on your timeline.
Last updated: May 2026
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About this calculator
The FIRE (Financial Independence, Retire Early) movement is built on accumulating a portfolio large enough that a safe withdrawal rate (SWR) covers all annual expenses indefinitely. The required 'FIRE number' depends on your FIRE type: Lean FIRE uses a 25× annual expenses multiplier (4% SWR), Fat FIRE uses 30× (≈3.3% SWR), and standard FIRE uses 27× (a small buffer above the classic 4% rule). The portfolio grows both from compounding on existing net worth AND from new annual savings, so the closed-form solution is: starting from FV = P × (1 + r)^N + S × ((1 + r)^N − 1) / r = T (target), solving for N gives N = ln((T + S/r) / (P + S/r)) / ln(1 + r), where P = currentNetWorth, S = annualSavings, r = investmentReturn / 100, and T = annualExpenses × multiplier. This is the standard formula for future value of an annuity with an opening balance, used by every FIRE calculator (Engaging-Data, Vanguard, MMM). Annual savings has dramatic leverage: doubling it can roughly halve the timeline at typical return rates, which is why Mr. Money Mustache's famous savings-rate table shows ~25 years at 25% savings rate but ~7 years at 75%.
How to use
Suppose you have $150,000 in net worth, save $30,000/year (after-tax), spend $40,000/year, target standard FIRE (27× multiplier), and expect 7% annual investment returns on a 60/40 portfolio. Step 1 — FIRE number T: $40,000 × 27 = $1,080,000. Step 2 — Savings perpetuity term S/r: $30,000 / 0.07 ≈ $428,571. Step 3 — Apply the closed-form: N = ln((T + S/r) / (P + S/r)) / ln(1 + r) = ln(($1,080,000 + $428,571) / ($150,000 + $428,571)) / ln(1.07) = ln($1,508,571 / $578,571) / 0.06766 = ln(2.6075) / 0.06766 = 0.9583 / 0.06766 ≈ 14.2 years. Switching to Lean FIRE (T = $1,000,000): N ≈ 13.3 years. Doubling annual savings to $60,000 at standard FIRE: S/r = $857,143, ratio = $1,937,143 / $1,007,143 = 1.9234, N = ln(1.9234) / 0.06766 ≈ 9.7 years — saving more is the most powerful lever.
Frequently asked questions
What is the difference between Lean FIRE, standard FIRE, and Fat FIRE?
Lean FIRE targets a portfolio of 25× annual expenses (a strict 4% withdrawal rate), suited for frugal retirees willing to keep spending minimal. Standard FIRE uses a 27× multiplier, offering a slight buffer above the classic 4% rule. Fat FIRE uses 30× annual expenses, targeting a roughly 3.3% withdrawal rate for those who want a comfortable lifestyle with built-in market volatility cushion. The higher the multiplier, the larger the nest egg required, extending your working years but dramatically reducing the risk of outliving your money.
How does savings rate affect time to financial independence in FIRE planning?
Savings rate is arguably the most powerful lever in FIRE planning because it affects two variables simultaneously: a higher savings rate means more money invested each year, and it often signals lower annual expenses, which reduces the FIRE number itself. Someone saving 50% of a $80,000 income needs only $40,000/year and a $1,000,000–$1,200,000 portfolio, whereas someone saving 10% needs $72,000/year and a portfolio nearly twice as large. Research by Mr. Money Mustache popularized the insight that going from a 10% to a 50% savings rate can cut the time to retirement from over 40 years to roughly 17 years.
Why does the FIRE calculator use a logarithmic formula instead of a simple division?
A simple division would only work if your portfolio grew by a fixed dollar amount each year, but investments grow exponentially — each year's gains earn their own future returns (compounding). The logarithmic formula ln((Target / Current) + 1) / ln(1 + r) correctly models this compound growth by inverting the compound interest equation A = P(1 + r)^t, solving for t. This means early progress feels slow but accelerates dramatically as the portfolio grows, which is why reaching the final 20% of your FIRE number can feel faster than the first 20%.