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Withdrawal Simulator

Monte Carlo simulation of retirement portfolio withdrawals. See how long your savings might last under market uncertainty.

Your Situation

Market Assumptions

Presets:

How It Works

This tool runs 500 independent Monte Carlo simulations of a retirement portfolio. Each simulation starts with your current savings and applies a sequence of random annual returns based on a normal distribution with your specified mean and standard deviation.

For example: with ¥20,000,000 in savings, withdrawing ¥800,000/year (4%) at 6% expected return with 10% volatility over 30 years: the simulation might show ~85% success. Try adjusting the withdrawal amount or return rate to see how it changes.

In each simulated year, the portfolio grows (or shrinks) by the random return, then your annual withdrawal is deducted. If the balance drops to zero or below in any year, the simulation is marked as a failure. Simulations that survive all retirement years are successes.

The results show the distribution of ending balances across all simulations, including the median, key percentiles, and the overall success rate — the percentage of simulations where the money lasted.

Disclaimer: This is a simplified simulation for educational purposes only. It does not constitute financial advice. Past performance does not guarantee future results. The Monte Carlo simulation uses random normally-distributed returns which may not reflect actual market behavior.

Withdrawal Simulator (Monte Carlo): Guide

Intent
Simulate retirement withdrawals with a Monte Carlo-style calculator. See how long your savings last with different withdrawal rates and market conditions.
What it does
Runs 500 Monte Carlo simulations of yearly withdrawals from a savings portfolio, using normally-distributed random returns to show the range of possible outcomes.
Key features
500 simulation runs, Success rate calculation, Percentile breakdown (10th/25th/50th/75th/90th), Best/worst case display
Privacy
Everything runs locally in your browser. No data is uploaded.
Best for
  • Estimating if your retirement savings will last given a withdrawal rate
  • Understanding the range of possible outcomes (not just one number)
  • Stress-testing withdrawal plans against volatile market conditions
Why this tool
  • Shows probability-based results, not a single deterministic projection
  • Percentile ranges give a realistic picture of best/worst/median cases
  • Local-only: no sensitive financial data leaves your device

How to use

  1. 1Enter your current savings and expected annual withdrawal.
  2. 2Set the expected annual return and volatility (standard deviation).
  3. 3Choose your retirement period in years.
  4. 4Run the simulation and review the success rate and percentile breakdown.

Common mistakes

  • A simplified simulation uses normally-distributed returns; actual markets have fat tails and serial correlation.
  • The 4% rule was based on US data; Japanese market conditions may differ significantly.
  • This does not include taxes, fees, or sequence-of-return risk adjustments.
  • More simulations or different assumptions would give different results.

Examples

4% rule test
Savings: ¥30,000,000 Annual withdrawal: ¥1,200,000 Return: 6% Volatility: 10% Years: 30 Check if the traditional 4% rule works for your scenario.
Conservative withdrawal
Savings: ¥50,000,000 Annual withdrawal: ¥1,500,000 (3%) Return: 5% Volatility: 8% Years: 40 Lower withdrawal rate → higher success probability.

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