BMR Calculator

How your BMR is calculated

We use the Mifflin-St Jeor equation, the predictive formula most dietitians treat as the default because it is more accurate for modern bodies than the older Harris-Benedict equation. For men it is 10 x weight in kg plus 6.25 x height in cm minus 5 x age plus 5. For women the last term is minus 161 instead, which reflects the lower average lean mass in women.

For example, a 30-year-old man who weighs 80 kg at 178 cm has a BMR of about 1,770 calories a day: 800 plus 1,112.5 minus 150 plus 5. A woman with the same height, weight and age comes out near 1,600 calories, because the formula subtracts 161 instead of adding 5. The result is calories per day, not per hour.

BMR versus TDEE

BMR is not the number to eat at. It only covers rest, so it ignores walking, working, training and even digesting food. To get the calories you actually burn in a normal day, your Total Daily Energy Expenditure (TDEE), you multiply BMR by an activity factor, from 1.2 for a desk-bound day with no exercise up to roughly 1.9 for hard daily training plus a physical job. The man above at a moderate activity level of 1.55 would burn about 2,740 calories a day.

Eating at your BMR is usually too low and can stall progress or cost you muscle. Use your TDEE as the basis for any calorie goal: eat below it to lose fat, above it to gain, at it to maintain.

What changes your BMR

BMR drops as you age, lose weight or lose muscle, since the formula scales with body mass and a younger body. Muscle is more metabolically active than fat, so strength training and a higher lean mass raise your resting burn over time, while crash dieting tends to lower it. The estimate is a starting point: real resting metabolism varies by roughly 10 percent between people with identical stats, so treat the number as a guide and adjust intake based on how your weight actually moves.