How we calculate

Every number on our calculators comes from a published equation or a research-based rule. This page lists them, where each comes from and where it stops being accurate. The calculators are for adults (18+) and give estimates, not medical advice.

Daily calories (TDEE)

Resting energy uses the Mifflin-St Jeor equation, the most reliable of the common predictive equations in a systematic review of healthy adults with and without obesity [1, 2]:

BMR (men)   = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
BMR (women) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Total expenditure multiplies it by an activity factor:

Targets by goal

• Lose fat: a pace of 0.5% of body weight a week, about 5.5 kcal per kg of body weight a day. Losing at 0.5–1% a week is the range recommended for keeping muscle, and the slower end keeps more of it [3, 4].
• Floor: the fat-loss target never goes below 1200 kcal for women or 1500 kcal for men, the lower bounds of standard low-calorie diets [5]. When the pace would go lower, we raise the target and say so. Less than that only under medical supervision.
• Build muscle: 10% above TDEE.

Why the scale slows down. Expenditure falls as you lose weight, so a fixed deficit loses less over time than the classic 7700 kcal per kg rule predicts [6]. Treat the number as a starting point: after two weeks, compare with your weight and change intake by 100–200 kcal.

Macros

• Protein is set per kilogram of body weight, as the research measures it: 1.6 g/kg to maintain, 1.8 g/kg to build muscle, 2.0 g/kg to lose fat. Gains from extra protein level off around 1.6 g/kg [7]; the ISSN recommends 1.4–2.0 g/kg, more during a deficit [8].
• Fat takes 25% of calories, inside the accepted 20–35% range [9].
• Carbohydrate takes the rest. 4 kcal per gram of protein and carbohydrate, 9 kcal per gram of fat.

One-rep max

The average of the Epley and Brzycki formulas, from sets of 1–12 reps [10, 11]. Above 12 reps every formula becomes unreliable.

Epley    1RM = weight × (1 + reps ÷ 30)
Brzycki  1RM = weight × 36 ÷ (37 − reps)

Known limits

• Predictive equations are within about 10% for most people, not everyone [2].
• Activity factors are textbook multipliers, not measurements, and people tend to rate themselves as more active than they are. If in doubt, pick the lower level.
• Calories from a food photo in the app are an estimate. Research on AI photo estimates finds errors of around 10% for energy in controlled conditions and larger for fat; checking against a food database reduces them [12, 13].
• Not for pregnancy, eating disorders, kidney disease or anyone under medical treatment for weight: ask your doctor.

Sources

1. Mifflin MD, St Jeor ST, Hill LA, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247. doi:10.1093/ajcn/51.2.241
2. Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005;105(5):775–789. doi:10.1016/j.jada.2005.02.005
3. 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
4. Garthe I, Raastad T, Refsnes PE, et al. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab. 2011;21(2):97–104. doi:10.1123/ijsnem.21.2.97
5. National Heart, Lung, and Blood Institute. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. 1998.
6. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826–837. doi:10.1016/S0140-6736(11)60812-X
7. 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
8. Jäger 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
9. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press; 2005.
10. Epley B. Poundage chart. Boyd Epley Workout. Lincoln, NE: Body Enterprises; 1985.
11. Brzycki M. Strength testing: predicting a one-rep max from reps-to-fatigue. J Phys Educ Recreat Dance. 1993;64(1):88–90.
12. Isobe T, et al. Nutrients. 2026;18:966. doi:10.3390/nu18060966
13. Yan R, et al. Commun Med. 2025;5:458. doi:10.1038/s43856-025-01159-0