The formula
Mifflin-St Jeor: 10 × weight + 6.25 × height − 5 × age + 5 (men), − 161 (women)
Where it comes from
Basal metabolic rate is what your body spends staying alive: breathing, circulating blood, maintaining temperature and repairing tissue. It accounts for roughly 60 to 70 % of what most people burn in a day, which is why it dominates any calorie calculation.
How to work it out by hand
- Multiply your weight in kg by 10
- Multiply your height in cm by 6.25 and add it
- Multiply your age by 5 and subtract it
- Add 5 for men or subtract 161 for women
What is worth knowing
Mifflin-St Jeor is the recommended formula because it was validated against modern, more sedentary populations; Harris-Benedict dates from 1919 and tends to run 5 % high. The 10 % margin of error is what matters in practice: it means a calculated 1,650 kcal could really be anywhere from about 1,485 to 1,815. Treat the number as a starting point and adjust it from what your weight actually does over two or three weeks. That feedback beats any formula.