This tool runs 1,000 simulated retirements to estimate how likely your portfolio is to last to age 100. Each simulation draws a different sequence of historical market returns and applies your spending rules month by month. The fan chart shows the spread of outcomes: the amber band covers the 10th–90th percentile range, the teal band the 25th–75th (the middle half), and the dark line is the median. The dotted red line is the worst path across all simulations.
Rather than assuming returns are random and independent each year, block bootstrap resamples chunks of actual history. A block of 12 months means the simulator randomly picks a calendar year from the Shiller dataset (1900–2024) and uses all 12 of its months together, then picks another year, and so on until it has filled your full retirement horizon. This preserves the sequence-of-returns risk that makes retirement planning hard: bad years cluster (1929–32, 1966–82 stagflation, 2008), and that clustering gets captured in the model. Longer blocks preserve more regime structure; shorter blocks increase randomness. The default of 12 months samples whole years, which is the cleanest way to use the historical record.
Each year you spend portfolio × withdrawal rate, but never less than the floor. If your portfolio grows, your spending rises with it; if it drops, spending drops too (down to the floor). This naturally cuts withdrawals in bad markets, which is why it scores better on success rate than a fixed withdrawal. A common way to set the rate is to use the current CAPE ratio (Shiller's Cyclically Adjusted P/E) as a guide — when markets are expensive, a lower rate is safer. At today's elevated valuations, 3.5–4% is a typical starting point.
Your initial withdrawal amount is set strictly by the withdrawal rate. This exact dollar amount is withdrawn every year regardless of portfolio performance. This is the classic "4% rule" approach. It is simple and predictable, but it ignores portfolio growth — you leave money on the table in good scenarios and can't cut back automatically in bad ones.
Michael Kitces's formulation of the Guyton-Klinger decision rules. Your initial withdrawal rate is locked at retirement — initial spend ÷ starting portfolio. Each year, your effective rate — current spend ÷ current portfolio — is compared to that locked rate. If it rises above 120% of the initial rate (portfolio has shrunk and you're now over-withdrawing), spending is cut 10%. If it falls below 80% (portfolio has grown and you're under-withdrawing), spending is raised 10%. If you're between the guardrails, spending holds steady. This produces a more stable income than CAPE dynamic, which adjusts every year, while still responding to sustained market moves in either direction.
Each year, spending is set to exactly amortize the portfolio to zero by age 100, using a PMT formula at an assumed 5% real return. As the portfolio grows or shrinks, next year's spending adjusts automatically — it is always a percentage of the current balance, not a fixed dollar amount. The 5% assumption is calibrated for equity-heavy portfolios; a 60/40 allocation would use roughly 4–4.5%, which would produce modestly lower withdrawals. VPW has no spend floor — in a severe crash your spending drops with the portfolio. The trade-off is a guaranteed 100% success rate: the portfolio never runs out because you always spend a fraction of what remains.