Is this plan robust, or just lucky?
A single projection shows only one possible path, and its result depends on the sequence of yearly returns. A more useful question is how often the plan holds up across many simulated futures—and how much it depends on favourable growth.
What the answer depends on
- Which assumptions the test varies, and which stay exactly as you entered them.
- The length of the plan — a longer horizon gives more chances to meet a bad stretch.
- How much of the outcome rests on investment growth rather than steadier income.
- The size and timing of withdrawals, especially in the early years of drawing down.
- The reserve, and whether it covers a poor stretch without selling at the wrong time.
Before a change, and after it
Run the test on the same plan before and after a change, so the only difference between the two runs is the change itself. A chance read on its own is hard to place; the movement between two runs of the same plan is the part you can actually reason about, which is why one change at a time is worth the patience.
Remember that the result describes the plan exactly as entered. Optimistic returns, understated spending, or missing costs will make the chance of success look better because the test varies market outcomes, not the quality of your inputs. A seemingly resilient plan may still rely on generous assumptions.
Questions worth testing
- How much does the chance move when spending rises by a tenth?
- Which single assumption, made more cautious, moves the result most?
- How does the chance differ when the plan ends at 90 rather than at 100?
- What happens to the result when the reserve is doubled?
How to read the result
The chance of success shows how often the plan succeeds across simulated futures based on your assumptions. It is not the probability of a real-world outcome or a market forecast. There is no target figure: the result describes the plan, not you, and a low value is not a judgement. Plan Resilience is a Worthifi Pro feature. This is a planning illustration, not investment advice.
How it works in the app
Plan Resilience replays the plan through 1,000 simulated market futures and counts how often it holds up. You get a chance of success, three outcomes across poor, typical and good markets, and a fan chart of net worth across every future.
- Open a plan and tap “Test your plan” under Plan Resilience.
- Wait for the 1,000 simulations to finish.
- Read the chance of success, the three outcomes, and the fan chart.
Requires Worthifi Pro
Model this yourself