What FIRE and the 4% rule are
FIRE stands for Financial Independence, Retire Early. The premise is straightforward: build an investment portfolio large enough that its returns cover your living expenses indefinitely, so paid work becomes optional rather than mandatory.
At the center of the movement sits the 4% rule, made famous by the Trinity Study (Trinity University, 1998). Researchers ran historical stock-and-bond portfolios and found that withdrawing 4% of the starting balance in year one and adjusting that dollar amount for inflation each year, a portfolio survived 30 years in the vast majority of scenarios. Flipped around, that means you need to accumulate 25 times your annual expenses, because 100% ÷ 4% = 25.
How your FIRE number is calculated
Your FIRE number is the target net worth:
FIRE number = annual expenses ÷ safe withdrawal rate
At a 4% rate that is simply annual expenses × 25. If you want a bigger safety margin, a 3.5% rate multiplies by 28.6, and a 3% rate by 33.3.
To estimate when you’ll arrive, this calculator simulates your portfolio month by month: it starts from your current savings, adds your monthly contribution, and applies your expected return until the balance meets or beats your FIRE number.
Worked example
Say your expenses are 40,000 per year and you use a 4% withdrawal rate:
- FIRE number = 40,000 ÷ 0.04 = 1,000,000
Now start with 100,000 invested, contribute 2,000 per month, and expect a 7% annual return. Simulating the growth, the portfolio crosses one million in month 191, or roughly 15 years and 11 months. If you’re 35 today, you’d hit FIRE around age 51.
| Item | Value |
|---|---|
| Annual expenses | 40,000 |
| Withdrawal rate | 4% |
| FIRE number | 1,000,000 |
| Starting balance | 100,000 |
| Monthly contribution | 2,000 |
| Return | 7% |
| Time to FIRE | ~15 years and 11 months |
Flavors of FIRE
There isn’t a single path. These are the most common variants:
| Type | Core idea |
|---|---|
| Lean FIRE | Very frugal lifestyle; a small FIRE number because expenses are minimal |
| Regular FIRE | Keep your current lifestyle at expenses × 25 |
| Fat FIRE | A comfortable life with no cutbacks; demands a much larger number |
| Coast FIRE | You already have enough invested; you can stop contributing and just let it grow to 65 |
| Barista FIRE | Part-time work covers some expenses while the portfolio finishes maturing |
The Coast FIRE figure the calculator shows answers a specific question: how much you’d need invested today so that, without adding another dollar, compound growth alone carries you to your FIRE number by age 65.
Assumptions and limits
This is an educational projection with a constant rate, not a crystal ball. Keep in mind:
- Inflation raises your expenses over time; use real (inflation-adjusted) returns if you want to think in purchasing power.
- Sequence-of-returns risk matters: a big drop right as you start withdrawing hurts far more than the same drop years later.
- Taxes on interest and gains reduce the net outcome.
- The 4% rule was calibrated for 30 years; for very early retirements (40+ years) many people use 3-3.5%.
Disclaimer: this tool is an educational projection only and is not financial advice. Talk to a professional before making decisions.
Frequently asked questions
What exactly is the 4% rule?
It’s the guideline that you can withdraw 4% of your portfolio in the first year of retirement and adjust that amount for inflation each year, with a high probability the money lasts at least 30 years. Its inverse, multiplying expenses by 25, gives you the target capital.
How much do I need to retire?
It depends entirely on your spending, not your salary. If you spend 30,000 a year, your FIRE number at 4% is 750,000; if you spend 60,000, it climbs to 1,500,000. That’s why cutting expenses accelerates FIRE twice over: it lowers the goal and raises your savings rate.
Is FIRE realistic?
For most people it doesn’t mean quitting at 35, but it does buy freedom: choosing projects, cutting hours, or taking sabbaticals. The real levers are savings rate and time, far more than investment return. A sustained savings rate near 50% of income is what makes the numbers work.