How the calorie estimate works
The Mifflin-St Jeor equation estimates your basal metabolic rate — the energy your body uses at complete rest. Multiplying BMR by an activity factor gives TDEE, the calories you burn on a typical day.
- kg — body weight in kilograms
- cm — height in centimeters
- age — age in years
- s — sex constant (+5 / −161)
- factor — 1.2 sedentary → 1.9 very active
More detail
Losing or gaining weight
Roughly 7,700 kcal equals one kilogram of body fat. Eating about 500 kcal below your TDEE each day targets a steady ~0.5 kg loss per week; 500 above supports a lean gain. Bigger deficits aren’t better — they cost muscle and are hard to sustain.
Why activity level dominates
For most people the jump from “sedentary” to “active” changes daily needs by 500 kcal or more — far more than small differences in the BMR formula. Be honest about your activity; overestimating it is the most common reason a plan stalls.
Practical tip. Use this as a starting point, then adjust from real results. If weight isn’t moving after two weeks, nudge intake by 100–200 kcal rather than trusting the formula over the scale.
Frequently asked questions
How many calories should I cut to lose weight?
About 500 kcal below your TDEE per day targets a steady ~0.5 kg/week loss, since roughly 7,700 kcal equals one kilogram of body fat. The "Lose weight" output above already applies this to your numbers — going much deeper isn't better and costs muscle.
What's the difference between BMR and TDEE?
BMR is the energy your body burns at complete rest; TDEE multiplies BMR by an activity factor (1.2–1.9) to estimate total daily burn including movement and exercise. TDEE, not BMR, is the number to compare against your food intake.
How accurate is this calorie estimate?
The Mifflin-St Jeor equation is a solid population-level estimate for healthy adults, but actual needs vary with body composition, health, and genetics — it's not medical or nutritional advice. Treat it as a starting point and adjust based on real weight-trend results.
Why does an output show “—” instead of a number?
Several reasons, and the note under the result says which one applies. Age, height, or weight at zero or blank: nothing can be computed. Age under 19: Mifflin-St Jeor was derived from adults aged 19–78, so below that the equation is extrapolation, not estimation — a plausible-looking number would be worse than none. And the “Lose weight” target alone shows “—” when subtracting the 500 kcal deficit would leave nothing to eat; that is arithmetic about the deficit, not about your age, and usually means the height or weight is wrong.