The 4% rule is a retirement income guideline stating that you can withdraw 4% of your portfolio in the first year of retirement, then adjust that dollar amount for inflation each year, and your money will statistically last at least 30 years. It is the most widely cited starting point in retirement planning — but it was built on historical data from a specific era, and current research recommends caution before applying it mechanically.
Where it comes from
Financial planner William Bengen published a landmark study in the Journal of Financial Planning in October 1994. Working from historical US stock and bond returns dating back to 1926, Bengen tested every possible 30-year retirement window and found that a portfolio split 50% between US large-cap stocks and intermediate-term government bonds could sustain a 4.15% first-year withdrawal, inflation-adjusted each year, through every historical period — including the Great Depression and the stagflation of the 1970s. The number was rounded to 4% and became the benchmark.
The Trinity Study, published in the AAII Journal in February 1998 by three professors at Trinity University in Texas, confirmed and expanded on Bengen’s findings. Using a range of stock/bond allocations and time horizons, the study found that a 4% withdrawal rate produced a 95%+ portfolio success rate over 30-year periods with a 50/50 portfolio. “Success” meant the portfolio still had money at the end.
How it works in practice
The mechanics are straightforward:
- Add up all your retirement savings
- Multiply by 4% — that is your first-year withdrawal amount
- Each subsequent year, take that same dollar amount and increase it by the prior year’s inflation rate
- Do not recalculate 4% of your remaining balance — the base dollar amount is fixed and grows with inflation only
| Portfolio size | 4% annual withdrawal | Monthly income |
|---|---|---|
| $500,000 | $20,000 | $1,667 |
| $750,000 | $30,000 | $2,500 |
| $1,000,000 | $40,000 | $3,333 |
| $1,500,000 | $60,000 | $5,000 |
| $2,000,000 | $80,000 | $6,667 |
These figures are before Social Security or pension income. Social Security replaces roughly 40% of pre-retirement income for average earners, which reduces how much you need from your portfolio.
The reverse calculation: how much do you need?
Multiply your planned annual spending by 25. That is your target nest egg under the 4% rule. This works because 1 ÷ 4% = 25.
- Spending $40,000/year → need $1 million
- Spending $60,000/year → need $1.5 million
- Spending $80,000/year → need $2 million
- Spending $100,000/year → need $2.5 million
These targets represent your total portfolio. If your Social Security benefit will cover $24,000/year, subtract that before multiplying: spending $60,000 with $24,000 from Social Security leaves $36,000 from savings, requiring a $900,000 portfolio.
What current research says about safe withdrawal rates
The 4% rule is not static. Morningstar’s 2025 annual retirement income research estimated the safe starting withdrawal rate for a 30-year retirement at 3.9% — slightly below 4% — for retirees seeking consistent inflation-adjusted spending with a 90% probability of not running out of money. Their prior estimates: 3.3% in 2021, 3.8% in 2022, 4.0% in 2023, 3.7% in 2024.
The fluctuation reflects changing expectations for bond yields, equity returns, and inflation. Many financial planners currently recommend 3%–3.5% as the more conservative floor, particularly for:
- Early retirees (retiring before 60) who face a 35–40 year horizon rather than 30
- Retirees with a high proportion of bonds in a low-yield environment
- Anyone retiring near a stock market peak when sequence-of-returns risk is elevated
Sequence-of-returns risk: the hidden danger
Sequence-of-returns risk is the single biggest threat to a fixed-withdrawal strategy. If markets fall sharply in the first 5–10 years of retirement — while you are simultaneously withdrawing funds — the portfolio never recovers at the rate it would have if the decline had come later.
To illustrate: two retirees each start with $1,000,000 and withdraw $40,000/year (4%). Both experience the same average annual return of 5% over 20 years. Retiree A gets strong returns early and weak returns late; Retiree B gets weak returns early and strong returns late. Retiree A ends with over $1.5 million. Retiree B may run out of money entirely by year 17. Same average return, opposite outcomes — because order matters when you are withdrawing.
Adjustments that improve durability
The 4% rule assumes rigid fixed withdrawals. Real retirees have flexibility:
- Guardrail strategy: set a ceiling withdrawal (e.g., 5%) and a floor (e.g., 3.5%). If the portfolio grows, you can spend a bit more; if it falls, cut back temporarily.
- Dynamic spending: reduce withdrawals by 10% in any year the portfolio drops more than 15%
- Delay Social Security: claiming at 70 instead of 62 increases your monthly benefit by roughly 24–32%, reducing how much you need from investments
- Part-time work in early retirement: even modest income ($10,000–$20,000/year) dramatically reduces portfolio stress in the critical early years
Common mistakes
Treating 4% as a guarantee. It is a historical success rate, not a promise. Bengen himself has said the rule was never meant to be used mechanically — it was a floor for planning.
Ignoring a longer time horizon. A 55-year-old retiree needs 35–40 years of portfolio longevity, not 30. The safe withdrawal rate for a 40-year horizon drops to roughly 3.3%–3.5% under most historical scenarios.
Recalculating 4% from the remaining balance each year. This is not the rule. The rule sets a first-year dollar amount and inflates it. Recalculating from your balance causes you to withdraw more in good years and less in bad — a different (and generally inferior) strategy.
Applying it to a stock-heavy or bond-heavy portfolio. The original research assumed a roughly 50/50 stock/bond split. A 100% bond portfolio or a 100% stock portfolio produces very different outcomes.
Getting started
Run the reverse calculation: estimate your annual retirement spending, subtract your expected Social Security benefit, and multiply the remainder by 25–28 (25 for 4%, 28 for 3.5%). That range is your portfolio target. If you are more than 10 years from retirement, the exact withdrawal rate is less urgent than building savings aggressively. If you are within 5 years, work with a fee-only financial planner to stress-test your plan against sequence-of-returns scenarios and choose a withdrawal rate matched to your actual retirement horizon.