The 4% rule is a starting point, not a guarantee. Enter your portfolio, spending, and how long you need it to last, and see the withdrawal rate you're really relying on.
The 4% rule comes from research (most famously the Trinity Study) testing historical U.S. market returns: withdrawing 4% of a portfolio in year one, then adjusting that dollar amount for inflation every year after, survived nearly all rolling 30-year periods in the historical record for a balanced stock/bond portfolio.
where r is your expected real return — the simulation repeats this year by year until the balance runs out or outlasts your horizon.
4% was calibrated to a 30-year retirement. If you're retiring early and need your money to last 40 or 50 years, a lower withdrawal rate (often 3–3.5%) is more commonly used. If your horizon is shorter, a higher rate can be reasonable.
This tool projects your balance using one constant expected return, so you can see the deterministic, best-guess arithmetic behind your withdrawal rate. Real markets don't return the same amount every year — a few bad early years (sequence-of-returns risk) can deplete a portfolio faster than a smooth average return would suggest, even if the long-run average return is the same. That risk is exactly what historical and Monte Carlo studies behind the 4% rule are designed to test, and a single constant-return projection like this one can't fully capture it.
Curious what portfolio size gets you to a 4% withdrawal rate at your actual spending? Check the FIRE Number calculator.