What is a safe withdrawal rate and how is it different from the 4% rule?

A safe withdrawal rate (SWR) is the percentage of your portfolio you can pull in the first year, then inflation-adjust, with a high probability the money lasts your whole retirement. The 4% rule is simply one famous SWR estimate calibrated to a 30-year horizon.

Your personal SWR depends on your time horizon, asset allocation, fees, flexibility, and other income like Social Security or a pension. A 60-year-old planning 30 years might comfortably use 4% to 4.5%; a 40-year-old planning 50 years might use 3.25% to 3.5%. The longer the horizon and the more rigid your spending, the lower the safe rate. There is no single universal number, which is why running your own scenarios matters more than memorizing a percentage.