FIRE Calculator: Find Out Exactly When You Can Retire Early
FIRE — Financial Independence, Retire Early — turns retirement from a vague dream into a math problem. Once your investments reach roughly 25 times your annual expenses, you can stop working forever. This guide explains the 4% rule, the three FIRE variants, and how to find your exact retirement age with our free calculator.
Try FIRE Calculator Free →What Is a FIRE Number?
Your FIRE number is the portfolio size that lets you live off investment withdrawals indefinitely. The standard formula is annual expenses × 25, derived from the 4% safe withdrawal rate. If you spend $40,000 a year, your FIRE number is $1,000,000. Spend $80,000, and it's $2,000,000. Note that the number depends on your expenses, not your income — a high earner who spends little reaches FIRE far faster than a higher earner who spends everything.
The 4% Rule Explained
The 4% rule comes from the Trinity Study, which analyzed historical US market data and found that withdrawing 4% of a stock/bond portfolio in the first year of retirement (then adjusting for inflation annually) survived virtually every 30-year period in history. Conservative planners use 3.5% or even 3% for longer retirements; aggressive ones use 4.5%. Our calculator lets you adjust the withdrawal rate from 2.5% to 6% to see how it changes your target.
Lean FIRE vs Fat FIRE vs Coast FIRE
Lean FIRE: retiring on a minimal budget — roughly 60% of typical expenses. Smaller target, reached years earlier, but little slack for luxuries. Fat FIRE: retiring with 150% or more of your current spending — first-class travel, no budget anxiety, but a much larger target. Coast FIRE: the most underrated milestone — you've saved enough that compound growth alone will fund a normal retirement at 65. After hitting Coast FIRE you only need to earn enough to cover current living costs; saving becomes optional.
Your Savings Rate Matters More Than Returns
The single biggest lever in FIRE math is your savings rate — the percentage of income you invest. At a 10% savings rate, retirement takes roughly 50 years. At 25%, about 32 years. At 50%, just 17 years. At 65%, around 10 years. This is why the FIRE community obsesses over cutting expenses: every dollar not spent both grows your portfolio and shrinks the target it needs to hit.
How to Use the Formly FIRE Calculator
1. Enter your current age and total invested savings. 2. Add your annual post-tax income and annual expenses — the gap becomes your monthly investment. 3. Set expected return (8% is the long-term stock market average), inflation (3%), and withdrawal rate (4%). 4. Read your results instantly: FIRE number, exact retirement age, and the ages you'll hit Coast, Lean, and Fat FIRE. Everything updates live as you move the sliders, and all math runs in your browser — your financial data never leaves your device.
Common FIRE Mistakes to Avoid
Ignoring inflation — always plan in real (inflation-adjusted) returns, as our calculator does. Forgetting healthcare — early retirees lose employer coverage years before government programs kick in. Underestimating expenses — track actual spending for 3 months before trusting your number. Going 100% stocks at retirement — sequence-of-returns risk means a crash in your first retirement years can break the 4% rule; most FIRE retirees hold 10-40% bonds.
Frequently Asked Questions
What is my FIRE number?⌄
Your annual expenses multiplied by 25 (using the 4% rule). If you spend $50,000 a year, your FIRE number is $1.25 million.
Is the 4% rule still safe?⌄
It remains the standard baseline, backed by historical data over 30-year retirements. For retirements longer than 40 years, many planners recommend 3.25-3.75% instead. Our calculator lets you test any rate.
What is Coast FIRE?⌄
Having enough invested that compound growth alone — with zero further contributions — will fund a normal retirement at 65. It's often reachable in your 30s and removes the pressure to save aggressively.
Does the calculator account for inflation?⌄
Yes. It converts your expected return to a real (inflation-adjusted) return, so all results are in today's money.
Is my financial data stored anywhere?⌄
No. The FIRE calculator runs entirely in your browser — nothing is uploaded or stored.