Start with a week you recognize.
Enter your usual weekly grocery spending, excluding restaurant meals if you do not want them in the estimate. For an irregular shopping schedule, add several weeks of purchases and divide by the number of weeks.
Treat the unused percentage as a question.
The example starts at 10% only to demonstrate the arithmetic. It is not a claim about your household or an average. Try a few values to see the range, then keep a record if you want a more grounded estimate.
Use the result to choose one change.
The estimate treats every grocery dollar equally, but an unused ingredient may cost more or less than the rest of your basket. It also assumes the same pattern for 52 weeks. Use it to consider a habit, such as checking cupboards before shopping, rather than treating the result as money you will definitely save.
