How does the 4% rule change with a shorter versus longer retirement horizon?

The 4% rule was calibrated for a 30-year retirement, so your safe withdrawal rate should flex with how long your money must last. For a shorter horizon — say you retire at 60 with a 30-year plan, or expect Social Security and a pension to take over later — you can often support 4% or even slightly more, because there are fewer years of withdrawals to survive. For a much longer horizon, like retiring at 40 with 50+ years ahead, historical and simulated studies suggest dropping to roughly 3.25–3.5% to keep failure rates low. The intuition: more years means more chances for a bad market sequence and more inflation to outrun. Other income sources also let you raise the rate. Don't apply 4% blindly — match the withdrawal rate to your actual horizon, then build in flexibility to adjust along the way.