Historical cycles + Monte Carlo, side by side
How long will your money actually last?
Not a 4% rule of thumb — a real simulation run against 97 years of actual market history, or a randomized Monte Carlo stress test. Change any number below and the chart updates immediately.
Runs your scenario starting from every year in 1929–2025 (97 real market cycles), including the Depression, 2008, and 2022.
Withdraw the same inflation-adjusted amount every year, regardless of performance. This is the classic "4% rule" approach.
Success rate
How this works
Every simulation draws from the same base dataset: annual real (inflation-adjusted) total returns for the S&P 500 and 10-year Treasury bonds, 1929–2025, built from Robert Shiller's dataset and NYU Stern's historical returns series. Returns are real, so every dollar in this tool — your savings, spending, and results — is already expressed in today's purchasing power.
Historical Cycles
This mode runs your exact scenario starting from every one of the 97 years in the dataset, in the order they actually happened. If your retirement is longer than the years remaining in the data, the sequence wraps back to the beginning. This is the same method FIRECalc uses, and it's the standard for a reason: real market history has autocorrelation and fat-tail crashes that synthetic models tend to understate.
Monte Carlo
This mode runs 1,000 randomized trials, where each year's return is drawn independently, with replacement, from the same 97-year dataset (a technique called bootstrap resampling). It preserves the real shape of historical returns rather than assuming a bell curve, but breaks the actual chronological sequence — so it can generate harder back-to-back-bad-year sequences than ever actually occurred, which is why Monte Carlo results usually run a few points more conservative than Historical Cycles for the same inputs.
Withdrawal strategies
- Fixed real dollar — withdraw the same inflation-adjusted amount every year. The classic "4% rule" is this strategy at a 4% initial rate.
- % of portfolio — withdraw a fixed percentage of the current balance each year. Mathematically can't hit zero, but income varies with the market.
- Guardrails — a simplified version of the Guyton-Klinger decision rules. Withdrawals stay fixed in real terms unless the withdrawal rate drifts more than 20% above or below your starting rate, at which point spending is adjusted 10% to bring it back in line.
What's simplified
Social Security is entered as a flat monthly amount in today's dollars rather than calculated from earnings history — use the estimate from your Social Security statement. This tool doesn't model taxes, required minimum distributions, healthcare costs, or state-specific rules. It's a planning aid, not financial advice.