How it's calculated
You choose a daily calorie total and what share of it should come from protein and from fat. Carbohydrate gets the rest. The calculator converts each share into grams and checks it against the Acceptable Macronutrient Distribution Ranges (AMDRs) set by the National Academies' Food and Nutrition Board.National Academies
An AMDR is the range of intake for an energy source that is associated with reduced risk of chronic disease while providing enough essential nutrients. For adults the ranges are:
| Macronutrient | Adult AMDR (% of calories) |
|---|---|
| Protein | 10–35% |
| Fat | 20–35% |
| Carbohydrate | 45–65% |
The protein and fat inputs are limited to their adult ranges. Carbohydrate is whatever is left, so the calculator warns you when it falls outside 45–65%.
This is general nutrition information, not medical advice.
The formula
- Calories from each macronutrient = daily calories × its percentage.
- Grams = protein calories ÷ 4, carbohydrate calories ÷ 4, fat calories ÷ 9. These are the general factors of 4, 4 and 9 calories per gram that FDA nutrition labeling uses.FDA (eCFR)
- AMDR in grams = daily calories × the range's low and high percentages, divided by the same factors.
- Protein per kilogram (optional) = protein grams ÷ body weight in kg, shown next to the adult RDA of 0.8 g per kg.
Worked example
On 2,000 calories a day at 20% protein, 30% fat and 50% carbohydrate, you would eat 100 g of protein, 250 g of carbohydrate and 67 g of fat. All three are inside the adult AMDRs.
Raising protein to 30% and fat to 35% on 2,500 calories leaves only 35% for carbohydrate, below the 45% floor:
Protein a day: 188 GRAMS · 219 G CARBS · 97 G FAT
Assumptions and limitations
- Adults only. The National Academies set different ranges for children: fat 30–40% at ages 1–3 and 25–35% at ages 4–18, and protein 5–20% and 10–30% for those groups.
- Ranges, not prescriptions. The AMDRs describe a healthy range for the population. Within them, the right mix depends on your health, activity and food preferences. People with diabetes, kidney disease or other conditions should get advice from their doctor or a registered dietitian.
- Carbohydrate floor. The adult RDA for carbohydrate is 130 g a day, based on its role as the brain's main energy source; the calculator flags splits below it.
- The 4-4-9 factors are general averages. FDA labeling rules also allow food-specific factors, so a label can differ slightly from this arithmetic.
- Under review. In 2024 the National Academies published a letter report on rethinking the AMDR framework.National Academies Until new DRIs are issued, the ranges above are the current published values.
Don't know your calorie number? Start with the calorie calculator. Our guide to BMI, calories and macros walks through all three.