Many calculators say you need 25 times what you spend in a year. That figure was sized for the worst 30-year stretch to retire into. Most retirements start in better years, last longer or shorter than 30 years, and get help from Social Security. The number that fits yours may be well under 25 times, or above it.
The usual answer to this question is 25 times what you spend in a year, which is the same thing as withdrawing 4% of your balance annually. It is a real finding, not a made-up number. What gets lost is what kind of finding it is.
It came from running retirements against actual market history, one starting each January, and asking which starting balance lasted through the worst of them. Counted that way, the worst 30-year stretch to retire into began in 1966, and it needed about 25 times spending. That is where the rule comes from.
Because retirements don't all start in a year like 1966 and don't all last 30 years, this site uses real US market history as a whole instead of one starting year: stock returns since 1871, after inflation, spent down year by year. Let a retirement start in any month and the hardest start is a different one, September 1929, the peak before the crash, which needed about 30 times. The middle of that same history is a very different number again, closer to 13 or 14 times spending, because most retirements are not the worst one. Different starts disagree with each other, and when money is coming out every year the order the good and bad years arrive in matters as much as the average.
Each lane below is its own plan, driven on 1,000 unique stretches of real US market history. Some or all of those 1,000 trips get to the end fully funded; the rest need a route change (a spending adjustment). Compare plans by editing or duplicating a lane; the pinned lane is a reference for other lanes.