How to Calculate Your FIRE Number
Your FIRE number is the portfolio size you need to retire early and never run out of money. Here's the exact math — from the simplest formula to the full spectrum of FIRE variants.
1. What is a FIRE number?
FIRE stands for Financial Independence, Retire Early. Your FIRE number — sometimes called your FI number or nest egg target — is the total value of your investment portfolio that allows you to live off investment returns indefinitely without running out of money.
The concept is simple: once your portfolio is large enough, you can stop working and let compound growth sustain your lifestyle. The hard part is figuring out exactly how large "large enough" really is.
2. The formula
Annual expenses — the total amount you need to live on each year in retirement, in today's dollars. This should include housing, food, transport, healthcare, travel, and any other regular spending. Be honest; most retirees spend close to their pre-retirement amount, at least in the early years.
Withdrawal rate — the percentage of your portfolio you plan to withdraw each year. The most widely cited rate is 4%, derived from the Trinity Study (see below).
3. The 4% rule explained
The 4% rule comes from a landmark 1998 study by three finance professors at Trinity University (often called the Trinity Study). They backtested portfolios of US stocks and bonds from 1926 onward and found:
- A portfolio of 50–75% stocks could sustain 30 years of 4% annual withdrawals with very high historical success rates.
- 4% is the maximum safe withdrawal rate for a 30-year retirement period, not an average.
- In many historical scenarios the portfolio actually grew over 30 years — the 4% figure is deliberately conservative.
The key insight: if your annual expenses are $50,000 and you withdraw 4% of your portfolio, you need a portfolio of $50,000 ÷ 0.04 = $1,250,000.
4. Lean, Standard, and Fat FIRE
Not all FIRE targets are equal. Three common variants:
Target = (expenses × 0.6) ÷ WR. A minimalist lifestyle at 60% of current spending — achievable much earlier, but requires strict budgeting.
Target = expenses ÷ WR. Maintains exactly your current lifestyle in retirement. The most common FIRE target.
Target = (expenses × 1.75) ÷ WR. A generous buffer for healthcare, travel, family support, or lifestyle upgrades in retirement.
There are also sub-variants: Coast FIRE (you've saved enough that compound growth alone reaches your FIRE number) and Barista FIRE (part-time work covers expenses, so you need a smaller portfolio). Both have dedicated calculators on this site.
5. Step-by-step example
Let's walk through a concrete calculation:
- Calculate annual expenses: add up housing, food, transport, healthcare, subscriptions, entertainment, and miscellaneous. Suppose your total is $50,000 / year.
- Choose a withdrawal rate: we'll use the classic 4% (0.04 as a decimal). Early retirees may want 3–3.5%.
- Calculate your FIRE number: $50,000 ÷ 0.04 = $1,250,000. This is your Standard FIRE target.
- Optional — calculate Lean and Fat targets:
- Lean: ($50,000 × 0.6) ÷ 0.04 = $750,000
- Fat: ($50,000 × 1.75) ÷ 0.04 = $2,187,500
- Track your progress: divide your current portfolio by your FIRE number to get your completion percentage. $120,000 ÷ $1,250,000 = 9.6%.
6. Choosing your withdrawal rate
| Rate | Multiplier | Best for |
|---|---|---|
| 3.0% | 33× | Retiring very young; 50+ year horizon |
| 3.5% | 28.6× | Conservative early retiree |
| 4.0% | 25× | Classic FIRE target; 30-year horizon |
| 4.5% | 22.2× | Flexible retiree with income backstop |
| 5.0% | 20× | Aggressive or short horizon (15–20 yr) |
Lower withdrawal rates require larger portfolios but provide much more safety for long retirements. If you retire at 35 and live to 90, your money needs to last 55 years — well beyond what the original Trinity Study tested. Many FIRE community members target 3.5% for this reason.
7. Coast FIRE as a milestone
Coast FIRE is the point at which your portfolio is already large enough that compound growth alone — without any future contributions — will grow it to your full FIRE number by retirement age.
Formula: Coast FIRE = FIRE Number ÷ (1 + r)years
Example: FIRE number $1,250,000, 5% real return, 30 years to retirement: $1,250,000 ÷ (1.05)³Ⱐ≈ $289,222. If your current portfolio exceeds $289,222, you've hit Coast FIRE and could theoretically stop all contributions.
Frequently Asked Questions
What is the simplest way to calculate a FIRE number?
Multiply your annual expenses by 25. This is the inverse of the 4% rule. If you spend $50,000 per year, your FIRE number is $1,250,000. Adjust the multiplier if you use a different withdrawal rate: multiply by 33 for 3%, or by 20 for 5%.
Is the 4% rule still valid in 2025?
The 4% rule was derived from 30-year US market data. For longer retirements (50+ years, common for early retirees), many financial researchers recommend 3–3.5% as a more conservative rate. The rule remains a useful benchmark, but early retirees should stress-test their plans with lower rates.
How do I account for Social Security or pension income in my FIRE number?
Subtract your expected Social Security or pension annual income from your total annual expenses before calculating your FIRE number. For example, if you expect $18,000/year from Social Security and your expenses are $50,000/year, your FIRE-dependent expenses are $32,000 — giving a FIRE number of $800,000 at 4%.
Should my FIRE number include inflation?
Using real (inflation-adjusted) returns, your FIRE number can be stated in today's dollars. The 4% rule and the formulas on this site use real returns, which means the math already accounts for inflation — you don't need to add a separate inflation adjustment.
What's the difference between FIRE and Coast FIRE?
Your FIRE number is the final portfolio target that can sustain indefinite withdrawals. Your Coast FIRE number is a much smaller portfolio that you could have today and let compound — with zero future contributions — to reach your full FIRE number by retirement age. Coast FIRE is a powerful milestone on the way to full FIRE.
Ready to calculate yours?
Five free calculators. Real-time results. No sign-up required.