Financial calculator

Retirement Monte Carlo Calculator

Simulate retirement portfolio outcomes with monthly contributions, retirement withdrawals, and portfolio periods that change over time.

Percentile lines are cross-sectional snapshots across simulations, not single paths. Dollar fields accept commas, and rate fields are entered as percentages.

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General Assumptions

Set the starting balance, time horizon, simulation count, and optional seed.

Initial retirement portfolio balance.

Projection horizon in years.

Higher counts produce smoother percentile lines.

Leave blank for fresh random draws. Enter a number to reproduce the same results later.

Accepted for compatibility. Results are currently shown in nominal dollars.

Contributions & Withdrawals

Contribute monthly before retirement begins, then switch to withdrawals.

Monthly deposits made before withdrawals begin.

Enter 25 to begin withdrawals in year 25. Set to 0 to begin immediately.

Turn this on to use a fixed annual dollar withdrawal instead of a withdrawal rate.

Enter 4 for a 4% annual withdrawal rate.

Portfolio Periods

Each period applies until the next start year. Add a new period whenever expected returns or volatility change.

Keep the periods in chronological order. The first period must start in year 1.

Chart & Output Options

Choose how to view the simulation and optionally overlay actual simulated paths.

Annual is the default chart. Monthly data makes sequence-of-returns risk easier to see.

Lognormal mode compounds monthly growth more realistically.

Overlay a few actual simulated portfolio paths on the chart.

Display retirement-phase drawdown statistics below the main summary.

The chart updates in the browser after the API run completes.

Results

Percentile bands are cross-sectional snapshots across simulations. Sample paths, when enabled, show individual simulated trajectories.

Waiting for simulation

Summary

Run the simulation to see the projected retirement outlook.

Median ending balance
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10th percentile ending balance
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90th percentile ending balance
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Ruin probability
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Ruin probability means the percentage of simulations where the portfolio reached $0 after withdrawals began.