The practical benchmark is 20 percent
For chain restaurants covered by U.S. menu-labeling rules, the familiar calorie number is not expected to match every serving exactly. The FDA uses a 20 percent margin as a compliance benchmark: a tested item generally may be treated as meeting the standard when its calorie content is within 20 percent of the posted figure. So a meal listed at 500 calories could test at about 600 and still fall within that benchmark.
That does not mean restaurants can choose a number at random and add 20 percent. They must have a reasonable basis for the figure, such as nutrient data for the recipe or laboratory analysis. The benchmark is about how the FDA evaluates accuracy, not a promise that every plate contains the printed amount.
Why the same item can vary
Calories are calculated from ingredients and portions, and both can shift in an operating kitchen. A scoop may be slightly larger, a sauce portion heavier, or one batch of an ingredient different from another. Even careful staff cannot make every serving identical, and a laboratory test measures the particular sample it receives—not every serving sold.
The number is therefore most useful as a consistent estimate for comparing choices, rather than a precise reading of one meal. A difference of a few calories is not meaningful; a repeated gap large enough to exceed the benchmark can matter for compliance. The underlying tradeoff is practical: menus provide a standardized guide, while restaurant food is assembled one portion at a time.
