How to Calculate Your FIRE Number (Retire Decades Early)

Retirement at 65 is a default, not a destiny. The FIRE movement (Financial Independence, Retire Early) treats that default as a math problem with a better solution.

Money buys back time. By slashing expenses and maximizing your savings rate, you can accumulate enough income-producing assets to cover your living expenses indefinitely. When passive income exceeds lifestyle costs, work becomes optional.

The Mathematics of Freedom: The Rule of 25

Your FIRE Number is the total portfolio size required to fund your lifestyle permanently without a W-2 paycheck. The standard method for calculating it is the Rule of 25.

How it Works

The Rule of 25 comes directly from the Trinity Study and its 4% safe withdrawal rate. If you can safely withdraw 4% of a portfolio each year, your portfolio must equal 25 times your annual expenses.

1. Calculate Your Future Expenses: Determine what it costs to fund your life for one year (housing, food, healthcare, travel). Say that figure is $60,000.
2. Multiply by 25: $60,000 x 25 = $1,500,000.

A $1.5 million portfolio invested in assets such as S&P 500 index funds achieves FIRE. Historical average returns of 7-10% generate enough gains to pay your $60,000 annual draw while principal stays ahead of inflation.

The Engine of Speed: Your Savings Rate

Your Savings Rate controls how fast you reach FIRE. Raw salary does not.

A household earning $200,000 but spending $190,000 runs a 5% Savings Rate. That pace stretches retirement out over 60 years, because the lifestyle cost demands an enormous sustaining portfolio.

A household earning $80,000 and living on $40,000 runs a 50% Savings Rate. With 7%+ annual investment returns compounding those savings, financial independence arrives in approximately 17 years from a starting balance of zero. That timeline is driven by investment performance, not savings accumulation alone.

The Easy Way: The Freedom Projector

Modeling compounding returns against dynamic inflation and fluctuating savings rates across decades requires serious calculation. Skip the spreadsheet and use our FIRE Calculator.

Enter your current age, current portfolio balance, annual income, and target savings rate. The engine instantly plots your compounding growth curve and outputs the exact year and age you cross the threshold of permanent financial independence.

Frequently Asked Questions

What is the difference between LeanFIRE and FatFIRE?

LeanFIRE means reaching independence on a frugal budget (for example, $40,000 per year in expenses requiring a $1M portfolio). FatFIRE means reaching independence while sustaining a high-end lifestyle (for example, $120,000 per year in expenses requiring a $3M+ portfolio). CoastFIRE means you have saved enough early that compounding alone carries your portfolio to a full retirement target, so you can stop contributing and simply cover daily expenses with a low-pressure job.

What about healthcare costs in early retirement?

Healthcare is the largest obstacle for Americans who retire before Medicare eligibility at age 65. You must build the cost of open-market coverage, such as an ACA marketplace plan, into your annual expense estimate. If healthcare runs $8,000 per year, that single line item adds $200,000 to your required FIRE number.

Results are estimates for informational purposes only. Consult a licensed financial professional before making financial decisions.

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