A Monte Carlo retirement-ruin simulator. Set your expected annual return, strategy volatility, inflation, and withdrawal rate, then read off the probability that a portfolio is depleted over a 5–50 year horizon.
Each curve assumes external cash flow (pension, part-time income, …) covers a fixed share of your spending — from 0% (the portfolio funds everything) to 100% (fully covered, never bankrupt). Everything is computed live in your browser.
Method. Each year, the portfolio is debited the inflation-adjusted
withdrawal (fixed real "4% rule" spending) and then grown by a random return drawn from
a lognormal (geometric) distribution calibrated so annual gross returns have mean
1+return and standard deviation volatility. A path is counted
as ruined the first year the balance hits zero. The probability of ruin is the
fraction of 2,000 simulated paths ruined by each horizon. The 10 colored
curves share the same return paths and differ only in how much of your spending external
cash flow covers. Portfolio presets use 30-year nominal annualized return & volatility
(Jun 1996–May 2026, source: lazyportfolioetf.com);
the 50/50 figures are derived from the same dataset's 60/40 and 100%-stock anchors.
Leverage. With leverage ratio L and annual
interest rate c, each year the equity return is L×(asset return) − (L−1)×c
(so volatility scales to L×σ) and the withdrawal scales to L× the base
rate. Any year whose levered loss exceeds 100% wipes the portfolio to zero. At L = 100%
this is identical to the unlevered model. Leverage is a high-risk option — use it only to understand the downside.