How to Calculate Your FIRE Number (And What It Really Means)

The FIRE movement — Financial Independence, Retire Early — comes down to one number: the amount you need invested before you can stop working forever. Calculate it wrong and you run out of money at 55. Calculate it right and you have freedom for life. Here's the exact math.

The 25x Rule: The Foundation of Your FIRE Number

Your FIRE number is 25 times your annual expenses. If you spend $40,000 per year, your target is $1,000,000. If you spend $60,000 per year, your target is $1,500,000. That's it — that's the core formula.

This comes directly from the 4% safe withdrawal rate, which is based on the Trinity Study. The study found that a portfolio of 50–75% stocks can sustain 4% annual withdrawals over a 30-year retirement without running out of money, across virtually every historical market period.

• Annual expenses × 25 = FIRE number
• $30,000/year expenses → $750,000 FIRE number
• $50,000/year expenses → $1,250,000 FIRE number
• $80,000/year expenses → $2,000,000 FIRE number
• $100,000/year expenses → $2,500,000 FIRE number

Why Annual Expenses Matter More Than Income

Your FIRE number is based on spending, not salary. A person earning $200,000 but spending $150,000 needs a $3.75M portfolio. A person earning $80,000 but spending $35,000 only needs $875,000. The gap between income and spending — your savings rate — determines how fast you get there.

The Early Retirement Adjustment: Why 4% May Not Be Enough

The Trinity Study was based on 30-year retirements. If you retire at 35, you're planning for a 50–60 year retirement. Many FIRE practitioners use a 3–3.5% withdrawal rate for very early retirement, which means a 28–33x multiplier instead of 25x.

• Retiring at 65+: 4% withdrawal rate (25x expenses)
• Retiring at 55–64: 3.5% withdrawal rate (28x expenses)
• Retiring at 45–54: 3.25% withdrawal rate (30x expenses)
• Retiring before 45: 3% withdrawal rate (33x expenses)

What to Include in Your Annual Expenses

Most people undercount their expenses when calculating their FIRE number. Make sure to include housing costs, food, transportation, healthcare (especially important before Medicare at 65), travel, subscriptions, irregular expenses like car repairs and home maintenance, and a buffer for lifestyle inflation.

How to Calculate How Long It Takes to Reach Your FIRE Number

Once you know your FIRE number, the timeline depends on your savings rate and investment returns. At a 50% savings rate with 7% average annual returns, you can reach FIRE in roughly 17 years. At 60% savings rate, that drops to about 12 years. At 70%, around 8 years.

Common FIRE Variants and Their Numbers

• Lean FIRE: Very frugal retirement, typically under $40k/year. FIRE number under $1M.
• Regular FIRE: Middle-class lifestyle in retirement, $40k–$80k/year expenses.
• Fat FIRE: Comfortable or luxurious retirement, $80k–$150k+/year expenses.
• Barista FIRE: Semi-retire with part-time work covering some expenses — you need a smaller portfolio.
• Coast FIRE: You have enough invested that compound growth alone will reach your FIRE number by traditional retirement age — you just need to cover current expenses.