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The most widely cited safe withdrawal rate is about 4% a year — the "4% rule." Here is where that number comes from, how it works, why researchers disagree about it, and how to apply it to your own retirement numbers.
Short answer
A safe withdrawal rate is the percentage of your retirement savings you can spend in the first year — then adjust for inflation each year after — with a low historical risk of running out of money. The best-known figure is about 4% per year, from William Bengen's 1994 research and the 1998 Trinity Study. On US historical data, a balanced portfolio following this rule survived at least 30 years in almost every case tested. It is a starting guideline based on past returns, not a guarantee.
In 1994, financial adviser William P. Bengen published "Determining Withdrawal Rates Using Historical Data" in the Journal of Financial Planning. He tested every 30-year retirement window in US market history and asked: what is the highest first-year withdrawal rate that never ran out of money over 30 years? His answer was about 4%, adjusted for inflation each year, for a portfolio of roughly half stocks and half bonds.
In 1998, three professors at Trinity University — Cooley, Hubbard and Walz — published a related study (now called the Trinity Study) that measured the historical "success rate" of different withdrawal rates and portfolio mixes. It reached a similar conclusion, and the shorthand "4% rule" stuck.
The mechanic that people most often get wrong: you do not withdraw 4% of your balance every year. You withdraw 4% once, in year one, and then increase that dollar figure by inflation each year regardless of what the market does.
The inverse is the 25x rule: because 4% is one twenty-fifth, a target pot is roughly 25 times the annual spending you want it to cover. $40,000 a year → about $1,000,000; $80,000 a year → about $2,000,000. It ignores taxes, fees and other income, so treat it as a rough target.
The 4% figure is a historical result under specific assumptions, so reasonable analysts land on different numbers when they change those assumptions:
Used well, the rule is a sanity check, not a rigid instruction. A practical approach is to estimate the annual spending you want your portfolio to cover, multiply by 25 for a rough target, and then stress-test it — a lower rate if you are retiring early or want more cushion, a willingness to trim spending in down years, and an allowance for taxes and fees the rule ignores.
You can put your own figures into Richify's FIRE calculator to see the pot a given spending level implies, and track progress toward it against your real assets in your net worth. For related concepts, see the index funds explainer.
Educational information, not financial advice. A safe withdrawal rate is a planning concept based on historical data; it cannot predict your own results, and it is not a recommendation of a specific rate for your situation. Consider a licensed financial adviser before making retirement decisions.
The 4% rule is a retirement-spending guideline: in your first year of retirement you withdraw 4% of your portfolio, then each following year you withdraw the same dollar amount adjusted for inflation — not 4% of the new balance. It comes from financial adviser William Bengen's 1994 study and was reinforced by the 1998 Trinity Study. In US historical backtests, a balanced stock-and-bond portfolio following this rule lasted at least 30 years in nearly every starting year tested. It is a planning starting point, not a guarantee.
It is contested. The original 4% figure was based on US historical returns over rolling 30-year periods. Bengen himself later argued the safe figure was higher — around 4.5% to 4.7% — once a portfolio is diversified beyond two asset classes. Other researchers have argued for lower starting rates in periods of high stock valuations, low bond yields, or longer life expectancy; Morningstar's annual retirement-income studies, for example, have published starting safe-withdrawal estimates in the low-3% to roughly 4% range in different years. Treat any single number as an estimate tied to a set of assumptions and a date, and check current reporting.
The 4% rule has a simple inverse often called the 25x rule: if you can live on a withdrawal of X dollars per year, you need roughly 25 times X invested (because 4% is one twenty-fifth). For example, $40,000 a year implies a target of about $1,000,000; $80,000 a year implies about $2,000,000. This is a rough planning figure that ignores taxes, fees, and any other income such as a pension or social security, so your own number will differ.
For an early retirement that could last 40 to 50 years rather than the 30 years the original research modelled, many planners cite a lower starting rate — often around 3.25% to 3.5% — to reduce the risk of running out over the longer horizon. There is no single agreed figure; the right rate depends on your time horizon, asset mix, flexibility to cut spending in bad years, and other income. This is educational information, not a recommendation of a specific rate for you.