March 5, 2026 ยท fireandretire.com

Why Monte Carlo Simulations Are Essential for Retirement Planning

Most retirement calculators show you a single projection based on average returns. The problem? Markets don't deliver average returns every year. Monte Carlo simulations solve this by modeling thousands of possible futures.

What Is a Monte Carlo Simulation?

A Monte Carlo simulation runs your retirement plan through thousands of randomly generated market scenarios, each with different sequences of returns. Instead of showing you one outcome, it shows you a distribution โ€” and most importantly, the probability your plan succeeds.

Why Sequence of Returns Matters

Two retirees with identical average returns can have very different outcomes depending on when the bad years hit. A major market crash in year 1 of retirement is far more damaging than the same crash in year 20, because you're selling shares at low prices to fund living expenses. This is called "sequence of returns risk."

How to Interpret Monte Carlo Results

  • 90%+ success rate: Very safe plan
  • 80โ€“90% success rate: Reasonable, consider small adjustments
  • Below 80%: Consider saving more, retiring later, or reducing expenses

Using Monte Carlo to Stress-Test Your Plan

Run your plan with pessimistic assumptions: lower returns (5% instead of 7%), higher inflation (4% instead of 3%), and longer life expectancy (95 instead of 85). If your plan still shows 80%+ success, you have a robust retirement strategy.

Run a free Monte Carlo simulation with Fire and Retire. Sign up free to access full simulation tools.

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