How to Calculate Your BMR (Basal Metabolic Rate) — With Examples

Your basal metabolic rate (BMR) is how many calories your body burns just keeping you alive — heart beating, lungs breathing, brain thinking, body warm. Lying in bed all day, that's what you'd burn.

The formula (Mifflin-St Jeor, 1990)

This is the formula nutrition researchers actually use:

Men: BMR = 10·weight(kg) + 6.25·height(cm) − 5·age + 5
Women: BMR = 10·weight(kg) + 6.25·height(cm) − 5·age − 161

Worked examples

30-year-old man, 75 kg, 175 cm:

BMR = 10·75 + 6.25·175 − 5·30 + 5 = 750 + 1093.75 − 150 + 5 = 1,699 kcal/day

28-year-old woman, 60 kg, 162 cm:

BMR = 10·60 + 6.25·162 − 5·28 − 161 = 600 + 1012.5 − 140 − 161 = 1,312 kcal/day

Why BMR matters

BMR is the foundation for every calorie target you'll ever calculate. TDEE (total daily energy expenditure) = BMR × activity multiplier. Your weight-loss deficit is calculated from TDEE.

Why your BMR isn't constant

It drops as you lose weight (less mass to maintain).
It varies with body composition — muscle burns more than fat.
It varies with thyroid health, sleep, and chronic stress.

This is why a calorie target set on day 1 won't work on day 90. Zafit recalculates yours every week from your latest weight + activity.

BMR vs RMR vs TDEE

Term	Means
BMR	Calories at complete rest, fasted, lying down.
RMR	Resting metabolic rate — slightly higher than BMR (includes digestion).
TDEE	BMR × activity factor — what you actually burn in a day.

Frequently asked

Is BMR the same as my calorie need?

No. BMR is your floor. Your daily need is BMR × activity multiplier (TDEE).

Should I eat less than my BMR?

Generally no. Eating below BMR for extended periods slows metabolism and tanks energy. Calculate TDEE and create your deficit from there.

Does BMR change with age?

Yes — it drops about 2% per decade after 20, mostly because we lose muscle mass with age.