How RepMacro Calculates Your Macros
Every number our calculators show comes from the rules on this page. Nothing is hidden, and the same rules apply on every calculator.
1. Resting calories (BMR)
By default we use the Mifflin-St Jeor equation, which estimates resting energy from weight, height, age and sex:
- Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
- Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
If you enter a body-fat percentage, we switch to Katch-McArdle, which uses lean mass instead: 370 + 21.6 × lean body mass (kg). The result card always shows which formula was used. Imperial inputs are converted with 1 lb = 0.4536 kg and 1 in = 2.54 cm before calculating.
2. Daily calories burned (TDEE)
BMR is multiplied by an activity factor:
| Activity level | Factor |
|---|---|
| Sedentary | 1.2 |
| Lightly active | 1.375 |
| Moderately active | 1.55 |
| Very active | 1.725 |
| Extra active | 1.9 |
3. Goal adjustment
| Goal | Calories | Protein |
|---|---|---|
| Cut | TDEE − 20% | 2.2 g/kg |
| Recomp | TDEE − 10% | 2.2 g/kg |
| Maintain | TDEE | 1.8 g/kg |
| Bulk | TDEE + 10% | 1.6 g/kg |
The calorie target is rounded to the nearest 10 kcal.
4. Protein
Protein is set first, in grams per kilogram, using the values above. Protein is set higher in a deficit because it helps preserve muscle when calories are low.
Reference weight at a BMI of 30 or more. Grams per kilogram of total bodyweight can give very high numbers for people with more body fat (for example, 330 g a day at 150 kg). When your BMI is 30 or above, we base protein on your goal weight if you entered one that is lower than your current weight, or otherwise on the weight that gives a BMI of 25 at your height. This is a practical adjustment rather than a clinical standard; the calculator tells you when it applies.
The protein calculator uses ranges instead of a single value: 0.8–1.0 g/kg for general health, 1.4–2.0 g/kg for regular exercise, 1.6–2.2 g/kg for muscle gain or fat loss, and a floor of 1.0–1.2 g/kg for adults over 65. It applies the same reference-weight rule.
5. Fat and carbs
Fat is set at 25% of target calories, inside the 20–35% range in the U.S. Dietary Reference Intakes. Carbs receive whatever calories remain. We convert calories to grams with the 4-4-9 rule (protein 4 kcal/g, carbs 4 kcal/g, fat 9 kcal/g), round each macro to a whole gram, and nudge carbs so the macros add up to within 10 kcal of the target.
Keto mode
The keto calculator reverses the order: net carbs are fixed at the limit you choose (20, 30 or 50 g), protein is set by the same goal rules, and fat takes all remaining calories. Fat is rounded so the macros add up to within 5 kcal of the target. If fat falls below half of total calories, we show a warning, because that is low for a ketogenic diet.
6. Warnings
- Fast weight loss: if your goal weight and timeline mean losing more than 1% of your bodyweight per week, we show a warning.
- Low carbs: if carbs fall below 50 g a day, we suggest lowering fat or raising calories.
Limits of any calculator
Equations like Mifflin-St Jeor estimate the average for people like you; your real expenditure can be noticeably higher or lower. Activity factors are broad. Treat your result as a starting point, follow it for two to three weeks, and adjust using your weekly average weight.
The calculators are not designed for people who are pregnant or breastfeeding, under 18, managing diabetes, kidney disease or another medical condition, or with a history of disordered eating. Please work with a doctor or registered dietitian instead.
Sources
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, 2005.
- Jäger R, et al. International Society of Sports Nutrition position stand: protein and exercise. Journal of the ISSN, 2017.
- Morton RW, 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. British Journal of Sports Medicine, 2018.
- Bauer J, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. JAMDA, 2013.
Change log
- October 30, 2026: added the Recomp goal, keto mode and the TDEE calculator.
- October 30, 2026: added pound and feet inputs, the BMI-based protein reference weight, the fast-loss warning and the protein calculator.
General information only, not medical advice.