Calorie / BMR / TDEE Calculator (Mifflin-St Jeor)

Enter age, sex, height and weight to get your BMR — the energy your body spends doing nothing at all — then pick an activity level for TDEE, your total daily expenditure, and a goal (cut, maintain or bulk) for a calorie target. Metric and imperial input both work; the imperial figures are converted and the formula itself is always run in kilograms and centimetres.

The equation is Mifflin-St Jeor, published in 1990: 10 × kg + 6.25 × cm − 5 × age, plus 5 for men and minus 161 for women. It replaced Harris-Benedict as the default recommendation because it fits modern bodies better — Harris-Benedict, revised though it was, runs roughly 60 to 140 kcal high across typical adults, and the gap grows with body mass. Even so, the systematic review that made Mifflin-St Jeor the standard found it landed within 10 percent of measured resting energy expenditure for about four people in five who were not obese, and fewer than that among those who were. Ten percent of an 1,800 kcal BMR is 180 kcal, which is already wider than the 300 kcal surplus this tool offers for bulking.

The activity multiplier is by far the largest source of error, and it is the one you choose by eye. For a BMR of 1,780, sedentary gives 2,136 and the athlete setting gives 3,382 — a spread of about 1,250 kcal, more than twice the size of the 500 kcal deficit a cut applies. If the resulting target does not match what actually happens to your weight over two or three weeks, the activity level is almost always the input to revise, not the formula.

Two structural limits are worth knowing. The equation takes total body weight, not lean mass, so it over-estimates for a heavy person carrying a lot of fat and under-estimates for a lean, muscular one; formulas built on lean mass, such as Katch-McArdle, handle those cases better but need a body-fat measurement. And the familiar arithmetic that turns a 500 kcal daily deficit into roughly half a kilo a week only holds at the start: expenditure falls as body mass falls, so the same deficit buys progressively less. None of this is medical advice — if you are pregnant, managing a metabolic or thyroid condition, or working under a clinician's plan, the number that matters is theirs, not this one.