What is Monte Carlo? Instead of assuming one fixed rate of return, Monte Carlo simulation runs 1,000 randomized scenarios using your expected return and volatility. The result is a probability of success -- the chance your portfolio lasts through retirement. A 70%+ probability is generally considered the minimum acceptable threshold.
Simulation Parameters
Total retirement savings
Percentage of initial portfolio withdrawn per year
Average annual return (e.g., 7% for balanced portfolio)
Volatility of returns (e.g., 12% for balanced portfolio)
How long your portfolio needs to last
Annual inflation (withdrawals increase by this amount)
Probability of Portfolio Survival
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Simulations Run
1,000
Successful Outcomes
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Failed Outcomes
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Median Final Balance
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Probability Fan Chart
Shaded bands show the range of outcomes across 1,000 simulations. The darkest band is the median (50th percentile).
Percentile Analysis at Key Years
Year
10th Percentile (Bad)
25th Percentile
50th (Median)
75th Percentile
90th Percentile (Good)
Withdrawal Rate Sensitivity
How success probability changes across different withdrawal rates (holding all other inputs constant).