How accurate are calorie counts?

Food labels have a margin

US rules treat a food as misbranded if its calories are more than 20% above the label value ^[1]. So a 200 kcal label can hold up to 240 kcal before it breaks the rule.

People under-report what they eat

In a well-known 1992 study of people who said they could not lose weight on a diet, participants under-reported their food intake by an average of 47% ^[2]. That was a small, specific group, but it shows how far memory can drift.

How accurate are photo calorie apps?

A 2023 systematic review of 52 studies found AI photo estimates had average calorie errors from 0.10% to 38.3% ^[3]. Errors were lower for single, simple foods. The authors said AI can match, and may beat, human estimates.

Why tracking still works

A systematic review found a consistent link between self-monitoring and weight loss, though the evidence quality was weak ^[4]. Tracking the same way every day gives you a trend you can act on, even when single entries are off.

Five ways to get closer

• Photograph or log before you eat, not later.
• Shoot from above, in good light, with the whole plate in frame.
• Add cooking oils, sauces and dressings: they are easy to miss.
• Weigh a food once to calibrate your eye, then estimate.
• Watch your weekly weight trend and adjust your target.