Your FIRE Number: The One Number That Changes Everything
Most retirement advice tells you to save a percentage of your income. 10%. 15%. 20%. It's the wrong frame. Your income doesn't determine when you can retire. Your expenses do.
Your FIRE number is the portfolio size at which your investments generate enough income to cover your life — permanently. Everything in retirement planning flows from this one calculation. And the formula is embarrassingly simple.
Calculate your retirement date
Enter your current savings, monthly contributions, and expenses to see exactly when you'll hit your FIRE number.
Use the FIRE Calculator →The formula
FIRE Number Formula
Annual Expenses ÷ Withdrawal Rate
Example: $60,000/yr ÷ 0.04 = $1,500,000
At a 4% withdrawal rate, your FIRE number is exactly 25× your annual expenses. Spend $40,000/year? You need $1M. Spend $80,000/year? You need $2M. The multiplier is just 1 ÷ 0.04 = 25.
Use 3.5% for longer retirements (the multiplier becomes ~28.6×). Use 4.5% for shorter ones (the multiplier is ~22.2×). The withdrawal rate you choose matters less than getting your expense number right.
Expenses drive your number more than income
This is the insight that changes how people think about FIRE. Every dollar you cut from monthly expenses reduces your FIRE number by $300 (at 4% withdrawal rate). Not $12. Not $120. $300.
The $1,000/month example
A higher income helps, but only if it translates to higher savings. Earn $200k and spend $190k? Same result as earning $80k and spending $70k. Lifestyle inflation is the enemy — earning more but maintaining the same savings rate means the same number of years to retirement.
FIRE number by monthly expenses and withdrawal rate
Lower withdrawal rates require a larger portfolio but give you more margin for error — especially important for early retirees.
| Monthly expenses | 3.5% WR | 4% WR | 4.5% WR |
|---|---|---|---|
| $3,000/mo | $1.03M | $900k | $800k |
| $4,000/mo | $1.37M | $1.20M | $1.07M |
| $5,000/mo | $1.71M | $1.50M | $1.33M |
| $6,000/mo | $2.06M | $1.80M | $1.60M |
| $7,000/mo | $2.40M | $2.10M | $1.87M |
| $8,000/mo | $2.74M | $2.40M | $2.13M |
| $10,000/mo | $3.43M | $3M | $2.67M |
Annual expenses = monthly × 12. FIRE number = annual expenses ÷ withdrawal rate.
What changes your FIRE number
Social Security income
Every $1,000/month in SS benefits reduces your FIRE number by $300,000 at a 4% rate. If you're retiring early, don't count on it yet — but it's a real buffer that appears in your 60s and makes the math significantly easier.
Part-time work or side income
Earning even $1,500/month in retirement cuts your portfolio withdrawal need by $450,000. This is the logic behind Barista FIRE — you don't need to fully fund your retirement if you're willing to cover some expenses with light work.
Paid-off home
Eliminating a $2,000/month mortgage or rent payment reduces your FIRE number by $600,000. The debate between paying off your mortgage early versus investing the difference is real, but a paid-off home is a meaningful expense reduction.
Geographic arbitrage
Retiring to a lower cost-of-living area — or another country — can cut expenses 30–50%. A lifestyle that costs $6,000/month in San Francisco might cost $3,000/month in Portugal or Mexico. That difference reduces your FIRE number by $900,000 at 4%.
Coast FIRE number vs. your full FIRE number
Your full FIRE number is the portfolio size that sustains you today. Your Coast FIRE number is the amount you need invested right now so that — without adding another dollar — compound growth will get you to your full FIRE number by a target retirement age.
Example: You need $1.5M to retire at 65. At 7% real returns, you need about $185,000 invested at age 35 to coast to $1.5M by 65 — without saving another dollar. If you have that, you just need to cover current expenses through work, not build wealth. Completely different mental model.
Calculate your Coast FIRE number →Frequently asked questions
What is a FIRE number?
Your FIRE number is the investment portfolio size at which you can stop working. The formula is simple: annual living expenses divided by your withdrawal rate. At a 4% withdrawal rate, a $5,000/month lifestyle requires a $1.5M portfolio. Hit that number and your portfolio theoretically sustains you indefinitely.
Does my FIRE number include my home equity?
Only if you plan to access it — through downsizing, a reverse mortgage, or renting it out. A paid-off home reduces your expenses (no rent or mortgage payment), which lowers your FIRE number. But the equity itself doesn't generate income unless you tap it. Most FIRE calculators focus on liquid investment portfolios, not total net worth.
How do I calculate my annual expenses accurately?
Look at 12 months of actual spending, not your budget. Most people underestimate by 15–20%. Include irregular expenses: car repairs, medical costs, travel, home maintenance. A common rule of thumb is to take your monthly spending and multiply by 14 instead of 12 to account for irregular costs. Also consider how expenses change in retirement — some go down (commuting, work clothes), some go up (healthcare, travel).
Does Social Security reduce my FIRE number?
Yes, significantly. If you expect $2,500/month in Social Security benefits starting at 67, that's $30,000/year you don't need your portfolio to cover. At a 4% withdrawal rate, that reduces your required portfolio by $750,000. If you're retiring early, SS is far away, so it shouldn't factor into your initial FIRE number — but it does make the math better once you hit your 60s.
What's the difference between lean FIRE and fat FIRE?
Just spending levels. Lean FIRE is retiring on $30,000–$40,000/year — frugal but doable in low cost-of-living areas. Fat FIRE is $100,000+/year — comfortable, flexible, no real lifestyle sacrifices. Barista FIRE and Coast FIRE are middle-ground strategies where you cover some expenses with part-time work instead of needing a fully funded portfolio. There's no right answer — it depends what lifestyle you actually want.
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