The 4% rule and safe withdrawal rates: what the calculator can—and can’t—tell you

“Can I withdraw 4% a year?” hides two different calculations. The commonly described rule takes 4% of the starting portfolio in the first year, then adjusts that dollar amount for inflation in later years. It does not simply take 4% of whatever the portfolio is worth every year. William Bengen’s original research studied historical U.S. stock-and-bond returns and rolling retirement periods; it was a historical test, not a promise about future markets (Bengen, “Determining Withdrawal Rates Using Historical Data,” Journal of Financial Planning, 1994).

How much can you withdraw from $500,000 under the 4% rule?

$20,000 in the first year, then that dollar amount raised with inflation. At a 4% initial withdrawal rate, a $500,000 portfolio produces a first-year planned withdrawal of $20,000. If inflation is 3%, the following year’s planned dollar amount becomes $20,600. The withdrawal is tied to the starting balance and then inflation-adjusted; market returns determine what remains in the account.

The safe-withdrawal calculator lets you enter the portfolio, initial withdrawal rate, assumed annual return, inflation and horizon. It applies a constant-return model year by year, showing an illustrative balance path and whether that particular set of inputs reaches zero before the chosen horizon.

Can a withdrawal calculator tell you a safe rate?

No — a constant-return projection cannot show sequence risk. The order of returns matters when withdrawals are happening. A poor early sequence can reduce the balance while withdrawals continue; later returns then act on a smaller base. A single constant annual return smooths away that sequence risk. It also does not account for taxes, fees, changing spending, asset allocation, health costs, or other income sources.

Historical withdrawal studies have their own boundaries too: the market history, asset mix, withdrawal timing, fees, inflation treatment and chosen horizon all affect the result. The cited Bengen paper analyzes historical U.S. data. It cannot establish that the same rate will work in another market period or for a particular household. Treat a calculator result as a scenario, not a retirement recommendation or guarantee.

To see how fees can change long-run compounding, compare assumptions with the investment fee-drag calculator. For a separate look at historical portfolio losses and uncertainty, read VaR, beta and drawdown explained. Educational information only—not financial, tax, or retirement-planning advice.

Is 4% guaranteed to last 30 years?

No. It is a rule of thumb informed by historical research under particular assumptions. Future returns, inflation, fees, taxes, asset mix and spending needs can differ. Past historical outcomes do not guarantee a future result.

Does this calculator model actual market history?

No. It applies the annual return and inflation assumptions you enter as a smooth projection. It does not replay historical sequences or model year-to-year volatility. Two portfolios with the same long-run average return can experience different withdrawal outcomes if the returns arrive in a different order.