Use a range, not one magic number
A projection becomes much more useful when it includes a conservative case, a base case, and an optimistic case. A single number can make the future feel more certain than it really is.
Match the assumption to the goal and the portfolio
A short-term goal with a cautious portfolio should not use the same assumption as a long-term, equity-heavy portfolio. The question is not "what return sounds good?" It is "what assumption fits the kind of portfolio and risk I actually expect to hold?"
| Good habit | Why it helps |
|---|---|
| Test a lower-rate case | Shows whether the goal still works when markets disappoint. |
| Keep the base case grounded | Prevents planning around a number that only works in unusually strong conditions. |
| Think about inflation separately | A large nominal balance may still buy less than expected in the future. |
Do not confuse a smooth projection with a smooth market
Calculators often show a clean upward curve because they use a constant return. Real investing does not feel like that. The market path is uneven, and that can change how comfortable or disciplined a plan feels in practice.
What makes an assumption "reasonable"?
Reasonable does not mean perfect. It means the rate is honest enough that the projection still has value if the future turns out less exciting than you hope. If the goal only works at the optimistic assumption, the plan is probably too fragile.
Simple routine for choosing a rate
- Pick a conservative case you can emotionally live with if markets are disappointing.
- Pick a base case that reflects your actual long-term investing approach.
- Pick an optimistic case only as an upper range, not as the plan itself.