The 4% rule is the foundation of almost every retirement calculation. Understanding it takes about 5 minutes, and it will change how you think about money, work, and what "enough" actually means.
8 min read · startinvesting.ai
The 4% rule says: if you withdraw 4% of your investment portfolio in your first year of retirement and adjust that amount for inflation each year, your money will last at least 30 years in almost every historical market scenario — including the Great Depression, the 1970s stagflation, and the 2008 financial crisis.
It was first formulated by financial advisor William Bengen in 1994 and later validated by the famous Trinity Study (1998) at Trinity University. They backtested withdrawal rates against actual US stock and bond market returns going back to 1926. The conclusion: a 4% withdrawal rate has a 95%+ historical success rate for 30-year retirements with a balanced portfolio.
The 4% rule gives you a simple formula for your retirement number:
FIRE Number = Annual Retirement Spending × 25
Because 4% × 25 = 100% of your spending. Simple.
If you plan to spend $60,000 per year in retirement, your FIRE number is $60,000 × 25 = $1,500,000. Once you have that invested in a diversified portfolio, you can withdraw $60,000/year indefinitely — at least historically.
Here's what the 4% rule means in practice, across three different withdrawal rate assumptions:
| Annual Spending | 4% (Standard) | 3.5% (Conservative) | 3% (Ultra-safe) |
|---|---|---|---|
| $30,000/yr | $750,000 | $857,000 | $1,000,000 |
| $40,000/yr | $1,000,000 | $1,143,000 | $1,333,000 |
| $50,000/yr | $1,250,000 | $1,429,000 | $1,667,000 |
| $60,000/yr | $1,500,000 | $1,714,000 | $2,000,000 |
| $80,000/yr | $2,000,000 | $2,286,000 | $2,667,000 |
| $100,000/yr | $2,500,000 | $2,857,000 | $3,333,000 |
Numbers rounded. FIRE number = Annual spending ÷ withdrawal rate.
The 4% rule works because a diversified portfolio invested in stocks historically returns about 7–10% annually in nominal terms. After inflation (~3%), that's a real return of roughly 4–7% per year.
If your portfolio earns 7% real and you withdraw 4%, the remaining 3% continues to compound. In most years, your portfolio actually grows even while you're withdrawing from it. The rule fails mainly in scenarios where markets crash severely in the first years of retirement — before the portfolio has time to recover.
The original Trinity Study was designed for a 30-year retirement — roughly retiring at 65 and living to 95. If you're planning for a 40–50 year retirement (retiring at 40 or 45), many researchers recommend a lower withdrawal rate:
The simplest approach for early retirees: use the standard 4% rule to know the minimum required number, but plan to build 10–15% extra buffer before you stop working.
Your FIRE number is directly tied to your spending. Reducing your annual expenses by $10,000 reduces your required portfolio by $250,000. This is why the FIRE community focuses so heavily on spending — it has a 25× multiplier effect on how much you need to save.
A few levers that have an outsized impact:
Calculate your FIRE number
See exactly when you can retire — in today's dollars
Enter your savings, contributions, and spending to get your exact FIRE timeline.
Open FIRE Calculator →What is the 4% rule?
The 4% rule says you can withdraw 4% of your investment portfolio per year in retirement without running out of money over a 30-year period. It was derived from the 1998 Trinity Study, which tested historical withdrawal rates against actual stock and bond market returns from 1926 onward.
How do I calculate my FIRE number using the 4% rule?
Multiply your expected annual retirement spending by 25. If you plan to spend $60,000/year in retirement, your FIRE number is $60,000 × 25 = $1,500,000. That's the portfolio size at which a 4% annual withdrawal equals your spending.
Is the 4% rule still safe today?
Research generally supports the 4% rule for 30-year retirements. For early retirees with 40–50 year horizons, many planners recommend 3–3.5% to provide more buffer. Current low-yield bond environments have also prompted some experts to suggest 3.3–3.5% as more conservative targets.
What happens if the market crashes early in my retirement?
This is called "sequence of returns risk." A major crash in your first 5 years of retirement has a disproportionately large impact. Strategies to mitigate this include keeping 1–2 years of expenses in cash, having part-time income flexibility, or using a 3.5% withdrawal rate instead of 4%.
Can I use the 4% rule for an early retirement at 40 or 45?
For a 40–50 year retirement, the 4% rule has historically worked but with less margin. Most early retirees use 3.25–3.5% as a safer withdrawal rate for very long retirements. Some also plan for part-time income in the early years to reduce portfolio withdrawals.
What's the difference between 3%, 3.5%, 4%, and 5% withdrawal rates?
Lower withdrawal rates require a larger portfolio but provide more safety. At 3%, your FIRE number is annual spending × 33.3. At 3.5%, it's × 28.6. At 4%, it's × 25. At 5%, it's × 20 — the most aggressive rate, suitable only for shorter retirements or those with other income sources.
For educational purposes only. Not financial advice. The 4% rule is based on historical US market data and does not guarantee future results. Individual circumstances vary — consult a qualified financial planner before making retirement decisions.