Most retirement “calculators” rely on linear assumptions of the portfolio rate of return. The problem with this approach is that in reality returns are never consistent from year-to-year. For instance a portfolio provide an average annual return of 8.0% over a certain period time. The sequence of the individual returns will have a dramatic affect on the portfolios final value. Monte Carlo simulation is a technique that attempts to overcome this shortcoming by randomizing the sequence of historical returns and projecting a range of probable outcomes. This document provides an introduction to Monte Carlo simulation for retirement planing.