What is a FIRE Number?
Your FIRE number is the answer to a simple question: How much money do I need to never have to work again? FIRE stands for Financial Independence, Retire Early—a movement built on the idea that with enough savings and smart investing, work becomes optional far sooner than traditional retirement age.
It's not about hating your job (though that's valid). It's about having options. The freedom to walk away from work that drains you. The ability to take risks, change careers, or simply spend your finite time on earth doing things that matter to you.
The math behind your FIRE number comes from the 4% rule: if you can live off 4% of your nest egg each year, your money should last 30+ years—and historically, it often lasts forever. Flip that around, and you need 25 times your annual expenses saved up. That's your FIRE number.
Spend $40,000 a year? You need $1,000,000. Spend $80,000? You need $2,000,000. The formula doesn't care how much you earn—only how much you spend.
The 25x Rule Explained
The 25x rule (also called the rule of 25) is elegantly simple: multiply your annual expenses by 25, and that's the amount of money you need invested to retire.
Why 25? It's the inverse of 4%. If you withdraw 4% of $1,000,000, you get $40,000 per year. The Trinity study found that this withdrawal rate, adjusted for inflation each year, had a 95% success rate over 30-year periods using historical market data going back to 1926.
Here's what the 25x rule looks like at different spending levels:
| Monthly Expenses | Annual Expenses | FIRE Number (25x) | Safe Monthly Withdrawal |
|---|---|---|---|
| $2,000 | $24,000 | $600,000 | $2,000 |
| $3,000 | $36,000 | $900,000 | $3,000 |
| $4,000 | $48,000 | $1,200,000 | $4,000 |
| $5,000 | $60,000 | $1,500,000 | $5,000 |
| $7,500 | $90,000 | $2,250,000 | $7,500 |
| $10,000 | $120,000 | $3,000,000 | $10,000 |
Notice something? Every $1,000 you can cut from monthly expenses reduces your FIRE number by $300,000. That's the power of the 25x multiplier—small lifestyle changes have massive impacts on how much you need to save.
Adjusting Your Withdrawal Rate
The 4% rule isn't sacred. You can adjust the withdrawal rate slider above to see how it affects your number:
- 3% (33x): More conservative. Better for early retirees who need money to last 50+ years, or those who want extra safety margin.
- 4% (25x): The classic rule. Historically reliable for 30-year retirements.
- 5% (20x): More aggressive. Might work if you have other income sources, a pension, or flexibility to reduce spending in bad years.
What Affects Your FIRE Number
Only two things determine your FIRE number: your expenses and your chosen withdrawal rate. That's it.
Your Monthly Expenses (The Big Lever)
This is the variable that matters most. Your FIRE number is directly proportional to your spending. Cut your expenses in half, and you cut your FIRE number in half.
When estimating expenses, think about what you'll actually spend to maintain your desired lifestyle in retirement, not what you spend now. Some costs go down (commuting, work clothes, that daily stress-eating habit). Others might go up (healthcare before Medicare, hobbies you finally have time for, travel).
Be honest, but don't over-pad. You can always adjust later. The goal is a reasonable estimate, not a worst-case scenario that makes FIRE feel impossible.
Your Withdrawal Rate (The Safety Dial)
A lower withdrawal rate means you need more money, but your portfolio is more likely to survive market downturns and last longer. A higher rate means you need less, but you're taking more risk.
Most FIRE practitioners stick with 3.5-4%. If you're retiring at 30 and need your money to last 60 years, lean toward 3.5%. If you're retiring at 50 with a pension kicking in at 65, you might be comfortable with 4.5%.
What About Income?
Notice that your income doesn't appear in the FIRE number formula. A doctor earning $400,000 and a teacher earning $50,000 have the same FIRE number if they spend the same amount.
Income affects how fast you reach your number (via your savings rate), but not the number itself. This is why FIRE is accessible to people at many income levels—it's about the gap between earning and spending, not raw income.
Your Savings Rate Matters More Than Income
Here's a counterintuitive truth: someone earning $60,000 and saving 50% will reach FIRE faster than someone earning $200,000 and saving 10%.
Why? Two reasons, and they both come down to saving and investing more of what you earn:
- Higher savings rate = more money invested each month. Obvious, but important.
- Higher savings rate = lower expenses = lower FIRE number. If you're living on 50% of your income, your target is much smaller than someone living on 90%.
The math is stark. At a 10% savings rate, you'll work about 51 years to retire. At 50%, it's roughly 17 years. At 70%, it's about 8.5 years. The savings rate dominates everything else.
This doesn't mean you should live on rice and beans in a van (unless that genuinely makes you happy). It means being intentional about spending—cutting ruthlessly on things you don't care about so you can spend freely on things you do.
Use our When Can I Retire? calculator to see exactly how your savings rate affects your timeline.
After You Know Your Number
Knowing your FIRE number is the first step toward achieving financial independence, not the last. Here's what to do with it:
It's a Target, Not a Prison Sentence
Your FIRE number isn't the minimum you need to survive—it's the amount at which work becomes optional. You can hit your number and keep working because you love it. You can "retire" and do part-time consulting. You can take a gap year at 80% of your number and see how it feels.
Financial independence is about options, not about following a rigid plan.
The Number Will Change
Your expenses will evolve. Kids grow up and move out. You might relocate somewhere cheaper (or more expensive). Health costs change. Interests shift. Recalculate periodically—maybe annually—and adjust your plan.
Next Steps
Now that you know your number:
- Use the Retirement Projector to see how your current savings will grow
- Check When Can I Retire? to find your timeline
- Try How Much to Save? to figure out your required monthly savings
- Read What is FIRE? to understand the movement behind the math
FIRE Is Global
The 25x rule works in any currency. If you spend €3,000/month in Europe, your FIRE number is €900,000. If you spend £2,500/month in the UK, it's £750,000. If you spend ₹50,000/month in India, it's ₹15,000,000. The math is universal—only the currency symbol changes.
This calculator supports 8 currencies: USD, EUR, GBP, JPY, CAD, AUD, CHF, and INR. Use the currency selector in the navigation bar to switch. Your selection is saved automatically and applied across all calculators.
Frequently Asked Questions
Yes, as a starting point. The 4% rule is based on historical U.S. market data and has a 95% success rate over 30-year periods. However, it's not a guarantee—it's a guideline. For early retirees (40+ year retirements), consider using 3.5% for extra safety. The key is flexibility: if the market tanks early in your retirement, being willing to cut spending temporarily dramatically improves your odds.
The original Trinity study looked at 30-year periods. For longer retirements, you have options: use a more conservative 3-3.5% withdrawal rate (28-33x expenses), plan to earn some income in early retirement, or build in flexibility to reduce spending during market downturns. Historically, portfolios using the 4% rule often grew over 30 years rather than depleting, suggesting it works for longer periods too—but there are no guarantees.
It depends on your age and risk tolerance. If you're 25, Social Security might look very different by the time you're eligible. If you're 50, you can probably count on something. A conservative approach: plan your FIRE number without Social Security, then treat whatever you get as a bonus that lets you spend more or provides extra cushion. You can create a Social Security account to see your projected benefits.
Healthcare is often the biggest wildcard for early retirees in the U.S. Before Medicare at 65, your options include ACA marketplace plans (subsidies are based on income, and early retirees often qualify), healthcare sharing ministries, COBRA from a former employer, or a spouse's plan. Budget $500-$1,500/month per person depending on your age, health, and location. Include this in your monthly expenses estimate.
This calculator uses real (inflation-adjusted) returns, so your FIRE number is expressed in today's dollars. You don't need to mentally add a buffer for inflation—it's already baked into the math. When you withdraw 4% per year, you adjust that amount for inflation, and the assumption of ~5% real returns (after inflation) accounts for this.
This is called sequence of returns risk, and it's real. A crash early in retirement hurts more than one later because you're selling shares at low prices. The 4% rule accounts for this historically, but you can add extra protection: build a cash buffer (1-2 years of expenses), be willing to cut spending in bad years, or keep some income streams active in early retirement. Flexibility is your best defense.
Yes. This calculator supports 8 currencies: USD ($), EUR (€), GBP (£), JPY (¥), CAD, AUD, CHF, and INR (₹). Use the currency selector in the navigation bar to switch. All calculations work the same regardless of currency—the math behind FIRE is universal. Your preference is saved automatically.