How to calculate what discarded food costs your household

Start with the amount actually discarded

Write down the product, its package price and the part you threw away. If a pack contains several equal items, use the share discarded. For a weighed product, compare discarded weight with the package weight in the same unit.

For example, losing one quarter of a package costing £8.00 represents £2.00 of that purchase. This is an illustrative calculation, not a measured saving. If you do not know the price, leave it unknown rather than inventing a precise figure.

Keep a comparable record

Choose a period such as four weeks and record consistently. Keep different currencies separate. Do not add grams to pieces or treat volume as weight without an appropriate product-specific conversion. Before It Expires keeps recorded units and currencies explicit.

• Distinguish a whole pack from the amount left in it.
• Use the price actually paid where available.
• Review repeated losses by product or habit.
• Treat missing entries as missing information, not zero waste.

Use a scenario to choose your next experiment

The calculator below takes your weekly estimate and a reduction you choose, then multiplies the difference across 52 weeks. It helps compare scenarios; it cannot predict your behaviour, future prices or guaranteed savings.

Try a smaller pack for one frequently discarded product, then compare the next period with your earlier record. Look at spending as well as discarded quantities: a smaller pack can have a different unit price. The practical result matters more than a neat percentage.