The 4% rule is the most widely cited guideline in retirement planning — and the mathematical foundation behind the entire FIRE movement. Here is where it comes from, what it actually says, and when you should use a different number.
Written by Mike Starr
Founder, StackedTomorrow · M.S. Organizational Management
Last Reviewed: August 2026
Educational Content Only. All content on this page is provided for informational and educational purposes only. It does not constitute financial, investment, legal, tax, or retirement advice. The calculators and projections shown are illustrative models — not predictions or guarantees of future performance. Past performance does not guarantee future results. Always consult a qualified financial professional before making investment or retirement decisions.
The 4% rule was not invented by a blogger or a financial advisor — it emerged from peer-reviewed academic research. The landmark paper was "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable" published in 1998 by three professors at Trinity University: Philip Cooley, Carl Hubbard, and Daniel Walz.
The researchers examined historical U.S. stock and bond returns from 1926 through 1995. They tested every possible 30-year retirement window within that dataset — so a retiree who happened to retire in 1929 (right before the Great Depression), in 1966 (before the stagflation era), or any other period — and asked a single question: what annual withdrawal rate would have kept the portfolio from running dry over a 30-year retirement?
Their finding: for a portfolio of 50–75% stocks and the remainder in bonds, a 4% initial withdrawal rate adjusted annually for inflation succeeded (the portfolio survived) in approximately 95–98% of all 30-year periods tested — including through the Great Depression, WWII, the 1970s stagflation crisis, and the 1987 crash.
The mechanics are straightforward. In your first year of retirement, you withdraw 4% of your total portfolio value. You then adjust that dollar amount — not the percentage — by inflation each subsequent year.
Example: $1,000,000 Portfolio
Your remaining portfolio — roughly $960,000 after year one — continues growing through market returns, funding future withdrawals.
Notice that after year one, you are withdrawing based on the original dollar amount (inflated), not 4% of the current portfolio value. This distinction matters: if markets crash 30% in year two, you do not reduce your withdrawal proportionally. You withdraw the same inflation-adjusted amount — which is why the cash/bond buffer strategy is important for managing sequence of returns risk.
The 25x rule is simply the 4% rule expressed as a savings target. Because 1 ÷ 0.04 = 25, you need 25 times your annual expenses invested to sustain withdrawals indefinitely at 4%.
Annual Expenses × 25 = Portfolio Target
| Annual Spending | Portfolio Needed (4%) | Portfolio Needed (3.5%) |
|---|---|---|
| $30,000 | $750,000 | $857,000 |
| $40,000 | $1,000,000 | $1,143,000 |
| $60,000 | $1,500,000 | $1,714,000 |
| $80,000 | $2,000,000 | $2,286,000 |
| $100,000 | $2,500,000 | $2,857,000 |
Use the FIRE Calculator to project when you will reach your target based on current savings and contributions.
The original Trinity Study tested 30-year retirements. If you retire at 40 or 45 — common in the FIRE community — you may need your portfolio to last 50 or even 60 years. The research does not extend with the same confidence to those longer time horizons.
Consider 3–3.5% as your planning withdrawal rate. The required portfolio is 15–28% larger, but the margin of safety for a 50+ year retirement is meaningfully better.
The original 4% rule applies well here. A 30-year horizon is close to the study parameters. Many financial planners consider 4–4.5% appropriate for this group.
If you can reduce spending by 10–15% during severe market downturns, you can safely use a slightly higher withdrawal rate because you are not rigidly locked into a fixed dollar amount regardless of portfolio conditions.
The Trinity Study found that portfolio composition significantly affected success rates. Counterintuitively, higher stock allocations performed better over 30-year periods — despite greater volatility — because stocks provide the growth needed to sustain inflation-adjusted withdrawals over decades.
| Stock / Bond Mix | 30-Year Success at 4% |
|---|---|
| 100% Stocks | ~95% |
| 75% Stocks / 25% Bonds | ~98% |
| 50% Stocks / 50% Bonds | ~80% |
| 25% Stocks / 75% Bonds | ~52% |
Most FIRE practitioners do not include Social Security in their 4% rule calculation — they treat it as a bonus that increases their margin of safety. However, if you retire at a traditional age and plan to collect Social Security, you should account for it.
The correct approach: subtract your expected Social Security income from your annual spending needs before calculating the required portfolio. If you spend $60,000/year and expect $20,000/year in Social Security, your portfolio only needs to cover $40,000 — requiring $1,000,000 at 4%, not $1,500,000.
For early retirees, Social Security income is decades away and uncertain. Most treat it as an inflation-adjusted bonus that may reduce withdrawal rates later in retirement, providing additional longevity protection.
Enter your current savings and monthly contributions to see exactly when your portfolio will support your target withdrawal rate.
Open the FIRE Calculator