Monte Carlo simulation models thousands of possible future outcomes using random sampling to assess the probability of different portfolio performance scenarios. It helps answer "what if" questions about retirement planning.
Run N simulations: for each, generate random annual returns from a distribution, compound over T years, measure outcomes
Running 10,000 simulations of a 30-year retirement with 4% withdrawals might show a 95% chance of not running out of money — giving you confidence in your withdrawal rate.
AllInvestView's Monte Carlo projection runs your portfolio across a thousand simulated paths. See also the FIRE guide and Safe Withdrawal Rate.