What the calculator computes
The 4% rule calculator locks the rate at 4%. Year-one income is 4% of the starting portfolio. Later years, in the original rule, raise that dollar amount with inflation and never re-read the balance. This page exists because people type “4% rule calculator” and the generic safe-withdrawal-rate page was not winning that query.
Bengen (1994) was a 30-year historical result. It is not a 50-year result, and it is not net of a 1% advisory fee. The calculator’s fee field and the 1,000-path band are there so 4% is not the only number on the screen.
When to leave 4%
Leave it when the horizon is much longer than 30 years — withdrawal rates by age. Leave it when spending can flex — 4% vs guardrails and the retirement guardrails calculator. Leave it when you wanted a different rate on purpose — the safe withdrawal rate calculator.
The study behind the number
Is the 4% rule still safe is 5,000 regime-switching lifetimes, rigid versus flexible. Use that when you want a success rate. Use the calculator when you want a first-year cheque.