What is Monte Carlo Retirement Simulator?
The Monte Carlo Retirement Simulator helps you assess the robustness of your retirement plan.
When to Use This Calculator
- Stress-testing a retirement plan against realistic market volatility instead of a single average-return assumption
- Understanding the probability your savings will last through retirement, not just a single projected outcome
- Comparing how different withdrawal rates change your plan's probability of success
- Deciding whether your current savings and contribution rate leave enough margin for a bad sequence of market returns
- Explaining retirement plan risk to a spouse or partner using probability rather than a single deterministic number
- Checking how a more conservative or aggressive portfolio allocation shifts your success rate
Steps:
- Enter initial investment and monthly contributions.
- Input expected return and years.
- Set withdrawal rate.
- View success rate and scenarios.
Formula
Success Rate = (Simulations Ending Above $0 ÷ Total Simulations) × 100, across thousands of randomized market-return scenarios
Use Cases
- Retirement planning
- Risk assessment
- Portfolio optimization
Key Benefits
- See if savings rate funds desired retirement lifestyle
- Understand compound growth over 20-40 year horizons
- Factor Social Security pensions and investment returns
- Adjust savings rate and age for optimal plan
Pro Tips
- Maximize 401k match for instant 100 percent return
- Plan for healthcare costs over 300k for couple
- Use 4 percent rule for withdrawal guideline
Common Mistakes to Avoid
- Underestimating needs by ignoring inflation
- Starting too late missing powerful compounding
- Wrong allocation as retirement approaches
Key Terms Explained
- 401k: Tax-deferred retirement account
- Compound Interest: Earning interest on interest
- Inflation: Rising prices eroding purchasing power
- Asset Allocation: Distribution across investments
Related Concepts
- Safe Withdrawal Rate: The withdrawal rate assumption is one of the biggest levers in your success rate — explore the trade-offs with our safe withdrawal rate calculator.
- FIRE Calculator: For a simpler, single-scenario projection of your target retirement number, see our FIRE calculator — useful as a baseline before stress-testing it here.
- Retirement Calculator: Our general retirement calculator covers traditional retirement planning inputs like age, contributions, and target income in more detail.
- Sequence of Returns Calculator: Understand specifically how the order of good and bad market years — not just their average — affects your portfolio with our sequence of returns calculator.
- Coast FIRE Calculator: If your simulation shows a strong success rate well before your planned retirement age, our Coast FIRE calculator can show whether you could stop contributing entirely and still coast to your goal.
Example
With $500K initial, $2K/month, 7% return over 30 years, your plan has approximately 85% success rate.
Interpreting Your Results
A standard retirement projection assumes the same average return every single year, but real markets don't work that way — returns vary widely year to year, and a bad sequence of returns early in retirement (a market crash right after you stop working) can permanently damage a portfolio even if long-term average returns turn out fine, a risk called sequence-of-returns risk. Monte Carlo simulation runs your plan through thousands of randomized market scenarios instead of one average path, and reports the percentage of scenarios where your money lasted (the success rate) — a 90% success rate means your plan survived in 9 out of 10 simulated futures. Most planners consider 85-95% a reasonable target range: 100% is often unrealistic and may mean you're over-saving or under-spending relative to what's needed, while below 75-80% suggests your plan has meaningful risk of running short and could benefit from a lower withdrawal rate, higher savings, or a later retirement date. Because these are simulated, not guaranteed outcomes, revisit the simulation periodically as real market conditions, your savings, and your spending actually unfold.