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 savings rate, spending level, and chosen FIRE target on your timeline.
About this calculator
The FIRE (Financial Independence, Retire Early) movement is built on the concept of 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×. Years to FIRE is then calculated using a logarithmic growth formula: Years = ln((FIRENumber / currentNetWorth) + 1) / ln(1 + r), where r = investmentReturn / 100. This is derived from the compound interest formula, isolating time as the unknown. A higher savings rate shortens the timeline by both growing current net worth faster and reducing annual expenses, compressing the FIRE number itself. The formula assumes contributions continue, though this simplified version uses net worth growth rather than explicit annual contributions.
How to use
Suppose you have $150,000 in net worth, spend $40,000/year, target standard FIRE (27× multiplier), and expect 7% annual investment returns. Step 1 — FIRE number: $40,000 × 27 = $1,080,000. Step 2 — Apply formula: ln(($1,080,000 / $150,000) + 1) / ln(1 + 0.07) = ln(8.2) / ln(1.07) = 2.104 / 0.0677 ≈ 31 years. Switching to Lean FIRE (25×): FIRE number = $1,000,000 → ln(7.67) / 0.0677 ≈ 30 years. Reducing annual expenses to $30,000 with Fat FIRE (30×): $900,000 → ln(7.0) / 0.0677 ≈ 28.6 years.
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%.