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Retirement Planner · Track 3
R1 of 3 — Result guides

Reading the fan chart and key metrics

The MC Outcomes tab is where the simulation speaks. Five charts and a set of KPI cards tell the story of your plan across 5,000 possible futures. Here is how to read them.

Portfolio value £2m £1m £0 Retire P90 — best 10% P50 — median P25 P10 — worst 10% Age 53 60 70 80 Success probability 91.2% ↑ Robust
The fan chart
1
P10 / P25 / P50 / P75 / P90 — what each line means

The five percentile lines show the portfolio value over time at five points in the distribution. P50 is the median — half of simulated paths end above it, half below. P10 is the 10th percentile — only 10% of paths are worse.

The fan width — the gap between P10 and P90 — shows how much uncertainty your plan has. A narrow fan means outcomes are consistent. A wide fan means the result depends heavily on which future you get.
2
A falling P10 line is the warning sign

If the P10 portfolio value falls to zero before the end of the horizon, your worst-scenario paths are running out of money. This is the signal to adjust — not the P50.

3
The retirement vertical line

The amber dashed line marks the retirement month. Portfolio growth before this line is the accumulation phase. Drawdown begins to the right of it.

The key metrics
4
Success probability

The percentage of 5,000 paths in which the portfolio funds the full horizon without running out. 91% means 4,550 paths succeed. 9% (450 paths) run out before the end.

Success probability is not a prediction — it is a stress test. A 91% result does not mean you have a 91% chance of being fine. It means your plan survives 91% of the historical return distribution used in the simulation.
5
What success probability thresholds mean

Above 90%: robust plan, limited adjustment needed. 80–90%: solid, minor improvements worth considering. 70–80%: plan needs attention — retire later, reduce spending, or increase contributions. Below 70%: significant changes required.

6
P50 final balance — not the target

The median final balance is often large and growing. This is not waste — it reflects the asymmetric nature of the simulation: paths that do well grow significantly, while failed paths are already at zero. The median is pulled up by the good paths.

Do not reduce spending just because the P50 final balance is large. You need that buffer to protect the P10 scenario.
7
Safe withdrawal rate

The maximum annual withdrawal as a percentage of opening retirement portfolio at which the plan achieves the configured ruin tolerance. It is calculated from your simulation results — not a generic rule.

8
Median shortfall months and % paths with shortfall

Shortfall months is the median number of months paths that fail run short by. % paths with shortfall is the proportion that fail at all. Together these give the severity and frequency of failure.

Track 3 · R1 of 3