Your basal metabolic rate (BMR) is the energy your body uses at complete rest. Multiply it by an activity factor and you get your total daily energy expenditure (TDEE) — roughly the calories needed to maintain your current weight.
The Mifflin–St Jeor equation
This calculator uses the Mifflin–St Jeor formula, widely considered the most accurate simple estimate. It combines your weight, height, age, and sex; the activity multiplier then scales BMR up to account for daily movement and exercise.
These are estimates, not prescriptions. Actual needs vary with body composition, genetics, and health. To lose weight, a moderate deficit below maintenance is typical — but consult a professional before making big changes.
A worked example
For a 30-year-old man who is 175 cm and 75 kg, Mifflin–St Jeor gives a BMR of about 1,699 calories: 10 × 75 + 6.25 × 175 − 5 × 30 + 5. At a “moderately active” multiplier of 1.55, his daily maintenance need (TDEE) is roughly 2,633 calories.
The same stats for a woman use −161 instead of +5, giving a lower BMR of about 1,533 and a proportionally lower TDEE. Bump the activity level from moderate to very active and the maintenance figure jumps by several hundred calories, which is why honest activity input matters.
Turning TDEE into a goal
Eating around your TDEE holds weight roughly steady. A deficit of about 500 calories a day is a common target for losing around a pound (0.45 kg) a week; a similar surplus supports gradual gain. Very aggressive deficits tend to backfire — they're hard to sustain and can cost muscle — so a moderate, steady gap usually wins.
Because TDEE is an estimate built on broad activity buckets, treat the number as a starting point. Track your weight over two to three weeks and adjust based on what actually happens, not on the formula alone.