BMR & TDEE calculator

BMR is what your body burns doing nothing at all — keeping your heart beating, your brain running, your temperature stable. TDEE multiplies that by an activity factor to estimate everything you burn in a day.

Mifflin–St Jeor men: BMR = 10w + 6.25h − 5a + 5 women: BMR = 10w + 6.25h − 5a − 161 (w in kg, h in cm, a in years) TDEE = BMR × activity factor

Which formula?

Mifflin–St Jeor (1990) validates better than the older Harris–Benedict for most adults, which is why it is the default here. Katch–McArdle uses lean body mass instead of total weight, so it is the most accurate of the three — but only if your body-fat estimate is any good.

The activity multiplier is the weak link

BMR formulas are accurate to roughly ±10% for most people. The activity factor is much cruder: the gap between “moderately active” and “very active” is 11%, and honest self-assessment is rare. Treat TDEE as a starting hypothesis, then adjust from what actually happens to your weight over two or three weeks.

The 3,500-calorie rule is an approximation

A pound of fat is often quoted as 3,500 kcal, giving the tidy “500/day = 1 lb/week”. Real bodies adapt — metabolic rate falls somewhat as weight drops, so the deficit that worked in month one produces less in month four. Expect the rate to slow and re-estimate periodically.