Monte Carlo Scenario Comparison
The Monte Carlo page now lets you stress-test multiple retirement scenarios side by side under the same simulated market conditions. Instead of running each scenario in isolation, the comparison uses shared random return sequences so the only differences in outcome reflect your plan design — not luck.
Why This Matters
A single Monte Carlo run tells you how your current plan might perform under market uncertainty. But when you're choosing between retiring at 62 vs 65, or debating fixed-percentage vs dynamic withdrawals, you need to see both options face the same sequence of good and bad years. Shared randomness removes noise and makes the comparison fair.
Getting Started
There are two ways to reach the comparison:
From the Monte Carlo page
- Go to the Monte Carlo page.
- Switch to the Compare Scenarios tab (next to "Single Scenario").
- Select up to 3 saved scenarios from the panel on the left. Your current profile is always included as the baseline.
- Adjust Market Volatility and Iterations if desired.
- Click Run Comparison.
From the Scenarios page
- Go to the Scenarios page.
- Select two or more scenarios using the checkboxes.
- Click the Stress Test button that appears in the toolbar — this opens the Monte Carlo comparison tab with your selected scenarios pre-loaded and the simulation runs automatically.
- Alternatively, open a scenario comparison first, then click Monte Carlo Comparison at the bottom of the comparison view.
Reading the Results
After the simulation completes, you'll see four sections:
Comparison Metrics Table
A side-by-side table showing key numbers for each scenario:
| Metric | What It Means |
|---|---|
| Success Rate | Percentage of simulations where your portfolio lasts through retirement. Above 80% is generally solid. |
| Median Portfolio at Retirement | The middle-outcome portfolio value at your retirement age. |
| Median Depletion Age | In failing simulations, the median age when funds run out. "Never" means most simulations survive. |
| Median Lifetime Withdrawal | Total inflation-adjusted withdrawals across retirement. |
| Median Total Tax Paid | Estimated total tax over your lifetime. |
- The best value in each row is highlighted.
- Scenarios show a delta from the baseline (e.g. "+3.2%" or "+$42K") so you can quickly see the impact of each change.
- Override badges (e.g. "Retire at 62", "dynamic", "+$10k/yr") appear under each scenario name so you can tell them apart at a glance.
Overlay Fan Chart
A chart showing the projected portfolio value over time for all scenarios on one axis. Each scenario is drawn in a distinct color with:
- A solid line for the median (P50) outcome.
- A shaded band for the P10–P90 range (the middle 80% of outcomes).
Use the Median Only toggle in the top-right corner to hide the bands and focus on comparing median trajectories. Click a scenario name in the legend to show or hide it.
Income Stability Chart
A line chart showing year-by-year withdrawal amounts during retirement:
- Solid line = median (P50) annual withdrawal.
- Dashed lines = P10 (bad markets) and P90 (good markets).
Wider gaps between P10 and P90 mean more income volatility. This is especially useful when comparing withdrawal strategies — for example, dynamic withdrawals will typically show a wider P10–P90 band but higher median income than the fixed 4% rule.
Auto-Generated Insights
Plain-language observations the app surfaces automatically. Examples:
- Which scenario has the highest success rate and by how much.
- Warnings for any scenario with a success rate below 70%.
- Trade-offs between highest success rate and highest lifetime income.
- Impact of different retirement ages or savings levels on the median portfolio.
Quick-Create Strategy Variants
If you don't have saved scenarios yet, use the Quick-create strategy variant panel in the scenario selector:
- Pick a withdrawal strategy from the dropdown (Fixed Percentage, % of Initial Balance, or Dynamic Guardrails).
- Click Create. This creates a new scenario identical to your baseline but with the selected withdrawal strategy.
- The new scenario is automatically added to your selection (up to 3).
This is the fastest way to do a pure withdrawal-strategy comparison without leaving the Monte Carlo page.
Simulation Parameters
Both the single-scenario and comparison modes share the same parameter controls:
- Market Volatility — annual standard deviation of returns. Use the preset buttons (Conservative 8%, Balanced 12%, Aggressive 18%) or drag the slider.
- Iterations — number of random simulations to run. 500 is a good balance of speed and accuracy; increase up to 2,000 for smoother results.
Tips
- Start with two scenarios that differ in exactly one dimension (e.g. retirement age) so you can isolate the effect of that change.
- Toggle "Today's $" at the top of the page to view results in inflation-adjusted dollars — useful for understanding real purchasing power.
- The comparison always includes your baseline profile so every scenario is measured against your current plan.
- Scenarios with a success rate below 70% trigger a warning insight — take these seriously and consider adjusting savings, retirement age, or strategy.