How this is calculated
- BMR — Mifflin-St Jeor. Your basal metabolic rate, the calories your
body burns at complete rest, uses the equation validated as the most reliable of the
common predictors:
BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5for males, and the same with− 161instead of+ 5for females. Imperial inputs are converted first (1 in = 2.54 cm, 1 lb = 0.4536 kg). - TDEE — activity multiplier.
TDEE = BMR × activity factor, using the standard multipliers:Level Describes Factor Sedentary desk job, little or no exercise ×1.2 Lightly active light exercise 1–3 days/week ×1.375 Moderately active moderate exercise 3–5 days/week ×1.55 Very active hard exercise 6–7 days/week ×1.725 Extra active physical job + hard daily training ×1.9 - Target calories.
target = TDEE + goal adjustment, where the adjustments are the widely used guideline defaults as of July 2026: −500 kcal/day for steady weight loss and +300 kcal/day for a lean muscle-gain surplus (these are directional conventions, not clinical prescriptions). The target is never allowed below 1,200 kcal/day — if the adjustment would go lower, the calculator floors it and shows a safety note. - Macros. Your split assigns a percentage of target calories to each
macronutrient, converted to grams with the standard Atwater energy factors:
protein 4 kcal/g · carbohydrate 4 kcal/g · fat 9 kcal/g. Sograms = target × % ÷ (4 or 9). The custom split must total exactly 100%. - Weekly projection. The rate line uses the classic
3,500 kcal ≈ 1 lb (0.45 kg)of body fat rule — a useful approximation, not a law: real-world loss slows as your body adapts and as water weight shifts, so expect the first weeks to run faster and later weeks slower than the projection.
What this doesn't model: body composition (very muscular or very lean bodies fall outside Mifflin-St Jeor's ±10% band), medical conditions, medications, pregnancy or breastfeeding, adaptive thermogenesis, or the thermic effect of specific foods. It's a solid starting estimate — adjust it against your real weight trend over 2–4 weeks.
Frequently asked questions
What is TDEE?
TDEE — total daily energy expenditure — is the total number of calories you burn in a day: your basal metabolic rate (the energy your body uses at complete rest) multiplied by an activity factor that covers exercise, work, and everyday movement. Eat roughly your TDEE and your weight holds steady; eat below it and you lose; eat above it and you gain.
How accurate is the Mifflin-St Jeor equation?
In comparison studies it is the most reliable of the common prediction equations for the general adult population, typically landing within about 10% of measured resting energy expenditure — which is why the Academy of Nutrition and Dietetics has recommended it over older formulas like Harris-Benedict. It is still an estimate: very muscular, very lean, or very heavy bodies can fall outside that range, so treat the result as a starting point and adjust from your real-world weight trend over 2–4 weeks.
How much protein do I need per day?
The RDA baseline is 0.8 g per kg of body weight, but for people who train or are dieting, common evidence-based guidance is roughly 1.6–2.2 g per kg (about 0.7–1 g per lb) to support muscle retention and satiety. The high-protein preset here (40% of calories) lands most people in that range; you can fine-tune it with the custom split.
Is 1,200 calories a day safe?
1,200 kcal/day is a commonly cited minimum below which it becomes very hard to meet nutrient needs, especially without medical supervision. This calculator never suggests a target below 1,200 kcal — if your goal adjustment would go lower, it floors the number and tells you. If you feel you need a faster rate of loss than that allows, work with a doctor or registered dietitian rather than cutting deeper.
This calculator is an educational estimate, not medical, nutritional, or fitness advice, and not a diagnosis or treatment plan. Individual needs vary; verify your plan with a qualified professional. No liability is accepted for decisions made from these results.