Short answer: Nutrition labels in the US are close, but not exact. The FDA does not test products before they are sold. Manufacturers calculate or lab-test their own numbers, and the FDA checks samples afterward. The rules allow calories, sugars, fat, saturated fat, cholesterol and sodium to be up to 20% higher than the label says, and naturally occurring nutrients like fiber and protein to be as much as 20% lower. Studies of packaged snacks have found calories about 4% above the label on average, well within those limits.
Many shoppers assume every Nutrition Facts panel has been checked by a government lab. It has not. This guide explains who sets the numbers, how the FDA verifies them, the legal accuracy limits (often called the “20% rule”), what independent testing has found, and how to use labels sensibly given the wiggle room.
Who Calculates the Numbers on a Nutrition Label?
The manufacturer does. The FDA sets the rules for the label format and accuracy, but it does not approve Nutrition Facts panels before products go on sale. Companies usually get their numbers in one of two ways:
- Laboratory analysis: sending samples of the product to a food testing lab, which measures fat, protein, carbohydrate, sodium and other nutrients using standard methods.
- Database calculation: adding up the nutrients in each ingredient using nutrient databases such as the USDA’s FoodData Central, adjusted for the recipe and cooking losses.
Calories on most labels are not measured directly. They are calculated from the amounts of protein, carbohydrate and fat using standard conversion factors (roughly 4 calories per gram of protein and carbohydrate, and 9 per gram of fat). That is one reason a label can differ from what a lab finds when it burns the food in a calorimeter.
How the FDA Verifies Nutrition Facts
FDA checks happen after products are on the market. Under its compliance programs, the agency collects products from stores and warehouses and has them analyzed. The regulation spells out the method: a sample is a composite of 12 packages, each taken from a different randomly chosen shipping case of the same lot, and tested using official AOAC laboratory methods. If the results fall outside the allowed range, the product can be considered misbranded, and the FDA can issue a warning letter or take further action.
In practice, the FDA samples only a small share of the many thousands of products on US shelves. Most enforcement focuses on clear problems, such as undeclared allergens or large, repeated errors.
FDA Accuracy Rules: The 80% and 120% Limits
The FDA sorts nutrients into groups with different accuracy rules. The table below summarizes 21 CFR 101.9(g).
| Nutrient group | Examples | Rule | What it means in practice |
|---|---|---|---|
| Class I: nutrients added to fortified or fabricated foods | Vitamins and minerals added to cereal, protein added to a bar | Must be at least 100% of the label value | If a cereal says 25% DV iron, it must contain at least that much. Extra is allowed. |
| Class II: naturally occurring nutrients | Protein, fiber, total carbohydrate, vitamins and minerals naturally in the food, unsaturated fats | Must be at least 80% of the label value | A label saying 5 g of fiber is compliant if the food has 4 g or more. |
| Nutrients to limit | Calories, total sugars, added sugars, total fat, saturated fat, trans fat, cholesterol, sodium | Can be no more than 120% of the label value | A 200-calorie snack can contain up to 240 calories. A label saying 400 mg sodium is compliant up to 480 mg. |
Notice the direction of each rule. The law protects you from getting less of the good nutrients and more of the ones to limit than the label says. It does not penalize a product that has more fiber or less sodium than stated. The FDA also allows for normal lab measurement error before taking action, so in practice the margin can be slightly wider.
Rounding Rules Add Another Layer
Label values are rounded in set steps, which is separate from the accuracy limits above:
| Nutrient | Rounding rule (per serving) |
|---|---|
| Calories | Under 5 can be shown as 0; up to 50 rounded to the nearest 5; above 50 rounded to the nearest 10 |
| Total fat, saturated fat, trans fat | Under 0.5 g can be shown as 0 g; under 5 g rounded to the nearest 0.5 g; 5 g and above to the nearest 1 g |
| Sugars, fiber, protein, carbohydrate | Under 0.5 g can be shown as 0 g; otherwise rounded to the nearest 1 g (“less than 1 g” is allowed for amounts under 1 g) |
| Sodium | Under 5 mg can be shown as 0 mg; 5–140 mg rounded to the nearest 5 mg; above 140 mg to the nearest 10 mg |
Rounding matters most when you eat several servings. A cooking spray can be labeled “0 calories” per quarter-second spray, and a spread can say “0 g trans fat” while containing a little. See how legal labels can still mislead.
How Accurate Are Nutrition Labels in Real Tests?
| Study | What was tested | What it found |
|---|---|---|
| NIH (Jumpertz et al., 2013) | 24 popular US snack foods, measured by calorimetry | Calories averaged about 4% higher than the label (median about 7 calories per serving), mainly from extra carbohydrate and slightly larger servings. All within FDA limits. |
| Tufts University (Urban et al., 2010) | 10 reduced-calorie frozen meals from supermarkets, and 29 reduced-calorie restaurant foods | Frozen meals averaged 8% more calories than stated. Restaurant foods averaged 18% more, with some items close to double. |
| Tufts University (Urban et al., 2011, JAMA) | 269 foods from 42 chain restaurants | Stated calories were accurate on average, but individual items varied widely. About 1 in 5 had at least 100 calories more than stated. |
The pattern is consistent: packaged food labels are usually close, while restaurant calorie counts vary much more because portions are prepared by hand. Chain restaurants with 20 or more locations must post calories and have a “reasonable basis” for them, such as lab analysis or nutrient databases, but a real plate can easily differ from the standard recipe.
What This Means for Shoppers
- Use labels to compare, not to count exactly. They are reliable for spotting big differences between products, such as 2 g vs 12 g of added sugar.
- Allow a margin if you track calories closely. Assuming packaged foods are within about 10–20% of the label is realistic. For restaurant meals, allow more.
- Check the serving size against what you eat. Serving size errors usually matter far more than lab variation. See how to read nutrition labels.
- Fortified nutrients are the most dependable numbers, because they must meet at least 100% of the label.
- Supplements follow different rules. Supplement Facts panels have their own compliance requirements. See how the FDA regulates supplements.
Frequently Asked Questions
How accurate are nutrition labels?
Usually within a few percent for packaged foods. FDA rules allow calories, sugars, fat and sodium to be up to 20% above the label, and naturally occurring nutrients like fiber and protein to be as low as 80% of the label. Independent tests of snack foods have found calories about 4% higher than stated on average.
What is the FDA 20% rule for nutrition labels?
It is the informal name for the FDA’s accuracy limits. Calories, sugars, total fat, saturated fat, trans fat, cholesterol and sodium cannot be more than 20% above the label value. Naturally occurring nutrients such as protein, fiber and carbohydrate must be at least 80% of the label value.
Does the FDA approve nutrition facts before products are sold?
No. The FDA sets the rules, but manufacturers are responsible for accuracy. The agency checks compliance afterward through sampling, inspections and follow-up on complaints.
Are calorie counts on nutrition labels accurate?
For packaged foods they are generally close, but they can legally be up to 20% low. Restaurant calorie counts vary more, and individual menu items have been found to contain 100 or more calories above the stated number.
Can I get a food tested myself?
Yes. Independent food labs will analyze a product for a fee. Consumer groups and journalists sometimes do this to check whether popular products match their labels.
Sources and Further Reading
- 21 CFR 101.9: Nutrition labeling of food (see paragraph (g) on compliance and (c) on rounding). eCFR.
- Food label accuracy of common snack foods. Jumpertz R et al. Obesity. 2013.
- The accuracy of stated energy contents of reduced-energy, commercially prepared foods. Urban LE et al. J Am Diet Assoc. 2010.
- Accuracy of stated energy contents of restaurant foods. Urban LE et al. JAMA. 2011.
- FoodData Central. US Department of Agriculture.
