Run Your Retirement Plan Through 5,000+ Random Market Scenarios
Average returns can be misleading. This Monte Carlo calculator stress-tests your retirement plan by simulating many possible return paths, including bad timing years.
Educational use only. This is a simplified model and not personalized financial advice.
What Is a Monte Carlo Simulation for Retirement?
A Monte Carlo retirement simulation tests your plan under thousands of possible market outcomes instead of just one “average return” path. In each run, returns change year by year in a random way based on your assumptions for expected return and volatility. The result is a probability of success: the percentage of scenarios where your portfolio lasts through your full retirement horizon.
This matters because retirement risk is not only about how much return you earn, but when you earn it. Two retirees can get the same long-term average return, yet one runs out of money because losses happened early. That is sequence-of-returns risk, and Monte Carlo analysis is designed to capture it.
How This Calculator Works
1) Accumulation phase (before retirement)
From your current age to retirement age, the model adds annual contributions and applies a random annual return. Contributions are assumed to grow with inflation to keep your real savings effort consistent over time.
2) Distribution phase (during retirement)
After retirement starts, the model subtracts your net spending:
- Retirement spending (inflation-adjusted) minus
- Social Security/pension income (also inflation-adjusted)
The remaining portfolio then experiences a random market return. If the balance reaches zero before your target end age, that simulation is marked as unsuccessful.
3) Final metrics
After all simulations are complete, you get:
- Success probability (likelihood your money lasts)
- Median ending balance (middle outcome)
- 10th percentile ending balance (more pessimistic scenario)
- 90th percentile ending balance (more optimistic scenario)
How to Interpret Your Results
A high success rate does not guarantee an outcome, and a lower success rate does not mean failure is certain. Think in terms of risk tolerance:
- 90%+: conservative plan with stronger safety margin
- 75%–90%: moderate risk, often acceptable depending on flexibility
- Below 75%: plan may need adjustments
Common adjustments include increasing annual savings, retiring a bit later, reducing retirement spending, or adjusting asset allocation.
Key Inputs That Matter Most
Spending level
Spending is usually the biggest lever in retirement outcomes. Even a modest reduction in annual expenses can significantly improve success odds.
Retirement date
Working 1–3 extra years has a double benefit: more contributions and fewer years drawing down the portfolio.
Expected return and volatility
Higher expected return can increase success, but higher volatility can hurt sustainability—especially early in retirement. Your assumptions should be realistic and tied to your planned asset mix.
Inflation
Inflation silently compounds over decades. Modeling retirement expenses in today's dollars and inflating them each year gives a more realistic projection.
Best Practices for Better Planning
- Run multiple cases: base, conservative, and optimistic assumptions.
- Stress-test with lower returns and higher inflation.
- Update your plan annually as markets and life circumstances change.
- Model flexible spending instead of fixed spending where possible.
- Coordinate this analysis with tax planning and withdrawal strategy.
Important Limitations
This calculator is intentionally simple. It does not model taxes, required minimum distributions, changing asset allocation over time, healthcare shocks, long-term care costs, or dynamic spending rules in detail. Use it as a decision-support tool, not a crystal ball.
For major retirement decisions, pair this output with a fiduciary financial planner and a comprehensive plan.