How accurate are calorie labels?

People assume the number on the packet is exact and their estimate is the sloppy part. Both carry error, and knowing roughly how much changes how you should use them.

Where error comes from

• Legal label tolerances
• Wrong database entries
• Portion estimation

Why the deficit still works

• You measure change, not absolutes
• A consistent method has a constant bias
• Your own weight trend corrects it

Labels have legal tolerances

Nutrition labels are not guarantees to the calorie. Regulators in the UK, EU and US all permit tolerance bands between the declared value and the measured one, because natural variation in food makes exactness impossible.

The practical result: a packet claiming 200 calories may genuinely contain somewhat more or less, and both are legal.

Databases add their own error

Crowd-sourced entries in the big consumer databases are often wrong — a duplicate with the wrong serving size, a value typed from the wrong column, a portion listed per 100 g when the label was per pack.

This is a real advantage of curated databases and of barcode scanning against the actual product rather than a search result.

Why your deficit still works

Because you are not measuring absolute intake, you are measuring change. If your logging is consistently 8% low, the target you set from your own two-week weight trend already absorbs it.

This is the argument for consistency over precision: log the same way every day and the errors become a constant you have already corrected for.

Where precision does earn its keep

Very lean people in a tight deficit, where the margin for error is genuinely small.

Calorie-dense foods measured by eye — oils, nut butters, cheese. A tablespoon of olive oil misjudged twice a day is a hundred calories.

Questions