Macro split calculator

How the split is worked out

1. Protein first. Grams = body weight in kg x the grams per kg you pick. 4 calories per gram.
2. Fat second. Calories x your fat share, divided by 9 calories per gram.
3. Carbs fill the rest. (Calories - protein calories - fat calories) divided by 4.

protein (g) = body weight (kg) x grams per kg
fat (g)     = calories x fat share / 9
carbs (g)   = (calories - protein x 4 - fat x 9) / 4

The 4, 4 and 9 are the general factors in the US labeling rules (21 CFR 101.9). Fiber is listed too, at the Dietary Guidelines goal of 14 g per 1,000 calories.

Where the choices come from

• Protein, 0.8 g per kg: the Recommended Dietary Allowance for adults, set to meet the needs of nearly all healthy adults. It is a floor for not training, not a target for building muscle.
• 1.4 to 2.0 g per kg: the International Society of Sports Nutrition position stand (Jager and colleagues, 2017), for people who exercise.
• 1.6 g per kg: where muscle gains from lifting leveled off, on average, in a meta-analysis of 49 trials (Morton and colleagues, 2018). That is why 1.6 is the standard choice.
• 2.4 g per kg: inside the 2.3 to 3.1 g per kg the position stand gives for lean, resistance-trained people eating below maintenance. It is for people who already lift and are already lean.
• Fat, 20 to 35% of calories: the adult range in the Dietary Guidelines for Americans. Researchers who write for lifters give 15 to 30% of calories while dieting (Helms and colleagues, 2014) and 0.5 to 1.5 g per kg (Iraki and colleagues, 2019). The tool warns when you fall under 20% or under 0.5 g per kg.
• Carbs: the Dietary Guidelines give 45 to 65% of calories and an RDA of 130 g. For people who lift hard, a bodybuilding nutrition review suggests at least 3 to 5 g per kg. The tool notes it when you fall under 3.

A worked example

A person who weighs 80 kg and eats 2,500 calories, at 1.6 g per kg protein and 25% fat:

• Protein: 80 x 1.6 = 128 g, which is 512 calories.
• Fat: 2,500 x 0.25 = 625 calories, divided by 9 = 69 g (621 calories).
• Carbs: (2,500 - 512 - 621) / 4 = 342 g.
• As shares of calories: protein 20%, fat 25%, carbs 55%. Fiber goal: 2.5 x 14 = 35 g.

Limits

• The protein and carb ranges come mostly from studies of lifters and athletes. For other people they are borrowed, and the RDA is the only figure aimed at everyone.
• The Dietary Guidelines ranges are old, and the National Academies themselves published a 2024 letter report asking whether the macronutrient ranges are still the right tool. Treat 20 to 35% as a sensible band, not a rule.
• Per-kilogram figures use total body weight. People with a lot of extra body fat may find them high; a dietitian can tailor it.
• These are not advice for pregnancy, kidney disease, or anyone on a medically supervised diet.

More: how to split your calories into protein, fat and carbs, the protein calculator and how much protein you need.

Sources

1. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025, Appendix 7: Nutritional goals for age-sex groups. PDF
2. Jager R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr 2017;14:20. doi:10.1186/s12970-017-0177-8
3. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med 2018;52(6):376-384. doi:10.1136/bjsports-2017-097608
4. Iraki J, Fitschen P, Espinar S, Helms E. Nutrition recommendations for bodybuilders in the off-season: a narrative review. Sports (Basel) 2019;7(7):154. doi:10.3390/sports7070154
5. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr 2014;11:20. doi:10.1186/1550-2783-11-20
6. Code of Federal Regulations, Title 21, section 101.9: Nutrition labeling of food (Cornell Legal Information Institute copy). 21 CFR 101.9
7. National Academies of Sciences, Engineering, and Medicine. Rethinking the Acceptable Macronutrient Distribution Range for the 21st Century: A Letter Report. 2024. doi:10.17226/27957

Written November 5, 2026, with the sources read that day. An estimate, not medical advice.