A scenario is a decision tool, not a daily scorecard. You do not need to rebuild it every time you buy something.
Useful reasons to review
- Income, rent, debt payments or another important regular amount changes.
- A one-off cost becomes likely.
- You are considering a decision the current scenario cannot answer.
- The assumptions are old enough that you no longer trust them.
If nothing important has changed, leave the scenario alone and use your attention elsewhere.
Tip: A short monthly or quarterly check may be enough. Review sooner when life changes, not because the calendar says you have failed to keep looking.