How it works
Basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive. This calculator finds it with the Mifflin-St Jeor equation, widely regarded as the most accurate BMR formula in general use today. Multiplying BMR by an activity factor gives total daily energy expenditure (TDEE) — roughly how many calories you burn in an average day including movement and exercise.
BMR (male) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
BMR (female) = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
TDEE = BMR × activity factor
A sustainable loss or gain is usually built from a moderate daily gap against TDEE — a 500 kcal/day deficit or surplus works out to roughly a pound (0.45 kg) a week, since that is approximately how many calories are stored in a pound of body fat. Larger gaps move faster but are harder to sustain and more likely to affect muscle mass and energy levels.
Worked example
A 30-year-old woman, 160 lb, 5'6" (66 in), moderately active.
- Convert to metric: 160 lb = 72.6 kg, 66 in = 167.6 cm.
- BMR = 10 × 72.6 + 6.25 × 167.6 − 5 × 30 − 161 = 1,462 kcal/day.
- Moderate activity factor: × 1.55.
- TDEE = 1,462 × 1.55 = 2,267 kcal/day.
Maintenance is about 2,265 kcal/day. A steady weight-loss target would be around 1,765 kcal/day (−500), and a steady gain target around 2,515 kcal/day (+250).
Figures are rounded to the nearest 5 kcal throughout — a calorie target precise to the unit implies an accuracy the formula does not have.
Common questions
Why does the formula need kilograms and centimetres?
Mifflin-St Jeor was published using metric units, so this calculator converts imperial entries to metric internally before applying it, then converts nothing else — calories are the same unit everywhere. Switching locale just changes which units you type in, not the underlying formula.
Which activity level should I pick?
Be honest about a typical week, not your best week. Sedentary means a desk job with little deliberate exercise; light is 1–3 light sessions a week; moderate is 3–5; active is daily exercise or a physically demanding job; very active combines both. Overestimating this is the most common reason a calorie target doesn't match reality.
Is TDEE the same as how many calories I should eat?
TDEE is your maintenance number — eating at it keeps weight roughly stable. Whether to eat above, at or below it depends on your goal, which is why this calculator shows loss and gain targets alongside it rather than just the one figure.