Calorie, TDEE, BMI, protein & water calculators

Methodology — How We Calculate

Most calculator sites hide their maths. Ours is on this page, in full, so you can check every number we produce — and see where the limits are.

Calories: BMR and TDEE

Equation: Mifflin–St Jeor (1990), the formula a 2005 review in the Journal of the American Dietetic Association found most accurate among the common equations.

  • Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
  • Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161

Activity multipliers: 1.2 (sedentary), 1.375 (light, 1–3 days/week), 1.55 (moderate, 3–5 days/week), 1.725 (very active, 6–7 days/week), 1.9 (extra active).

Goal adjustments: maintain +0, lose −500, lose faster −750, gain +300 kcal. Targets are never set below 1,200 kcal a day.

Macro splits (protein / carbs / fat, % of calories): lose and lose-faster 40/30/30, maintain 30/40/30, gain 30/50/20. Protein and carbs are 4 kcal per gram; fat is 9 kcal per gram.

Weight change: 7,700 kcal per kg of body weight change — a planning approximation, not a promise; real change is slower and non-linear.

BMI

BMI = weight (kg) ÷ height (m)². Categories are the standard World Health Organization adult bands: under 18.5 underweight, 18.5–24.9 healthy, 25.0–29.9 overweight, 30.0+ obese. The healthy range for your height is the weight span producing a BMI of 18.5–24.9 at your height. BMI is a screening statistic: it does not diagnose health, and it cannot tell muscle from fat.

Protein

Targets are grams per kilogram of body weight per day, by goal: build muscle 1.6–2.2, lose fat 1.8–2.4, endurance 1.2–1.6, maintain 1.2–1.6. These ranges follow sports-nutrition position stands and meta-analyses (for example the International Society of Sports Nutrition position stand). The RDA of 0.8 g/kg is a minimum to prevent deficiency; our maintain range is written for generally active adults, which is who this site serves.

Water

Base rule: 35 ml per kg of body weight, plus activity top-ups of 350 ml (~30-minute light session), 600 ml (~1 hour), 900 ml (long or hot session). For reference, the National Academies’ adequate intake for total water (food + drink) is about 3.7 L/day for men and 2.7 L/day for women.

What our numbers are — and are not

Every result here is an estimate built from population averages. Individual energy expenditure measured in a lab can differ from a formula by 10–20% or more, and short-term weight change tracks glycogen and digestion as much as fat. Use our numbers as a starting point, compare them with your real trend over 2–4 weeks, and adjust from there. When in doubt, talk to a professional — and read the disclaimer.