Which formula should I trust?

Mifflin-St Jeor; ADA reviews found it within 10% of measured values more often than Harris-Benedict. We show both so you can see the spread.

Is BMR the same as RMR?

Nearly. Resting metabolic rate is measured under slightly less strict conditions and typically runs a few percent higher than strict basal rate.

Why does BMR drop when I diet?

Adaptive thermogenesis: prolonged deficits lower hormone levels and spontaneous movement, reducing actual expenditure below what static equations predict.

Health

BMR Calculator

What this does

Estimate your basal metabolic rate; the calories your body burns at complete rest; using Mifflin-St Jeor with a revised Harris-Benedict comparison.

Enter your details

Runs in your browser

How to use it

Using the bmr calculator

01
Select sex
The equations differ by a constant term calibrated separately for men and women.
02
Enter weight, height and age
Use metric units: kilograms for weight, centimetres for height, whole years for age.
03
Compare the two rows
The main figure is Mifflin-St Jeor; the second row shows the revised Harris-Benedict value for reference.

Good to know

What BMR actually represents

Your basal metabolic rate covers breathing, circulation, cell repair, hormone production and brain function; typically 60–70% of total daily energy expenditure in sedentary people. It is the floor beneath every activity multiplier.

Why age matters

The −5A term subtracts five calories per year of age. Muscle mass tends to decline with age, and since muscle is metabolically expensive tissue, resting burn falls accordingly; one reason appetite needs shift decade by decade.

From BMR to real life

Multiply BMR by an activity factor (1.2–1.9) to reach TDEE.
Never eat below BMR for extended periods without professional guidance.
Recheck after significant weight changes of more than ~5 kg.

How it's calculated

The math behind this calculator

Men:   BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
(W kg, H cm, A years)

The primary estimate uses the Mifflin-St Jeor equation, published in 1990 and validated by the American Dietetic Association as the most accurate predictive formula for resting metabolic rate in the general adult population.

A revised Harris-Benedict row shows the older classic equation for comparison. When the two agree closely you can be confident in the estimate; wide gaps usually reflect unusual body compositions.

Assumptions & limitations

Healthy adult with typical body composition.
Measured at true rest; no digestion, exercise or stress.
Estimate only; indirect calorimetry is the clinical gold standard.

Worked example

A 30-year-old man weighing 80 kg at 180 cm has a Mifflin-St Jeor BMR of about 1,780 kcal/day; the energy his body spends simply keeping organs running.

FAQ

Frequently asked questions

Which formula should I trust?: Mifflin-St Jeor; ADA reviews found it within 10% of measured values more often than Harris-Benedict. We show both so you can see the spread.
Is BMR the same as RMR?: Nearly. Resting metabolic rate is measured under slightly less strict conditions and typically runs a few percent higher than strict basal rate.
Why does BMR drop when I diet?: Adaptive thermogenesis: prolonged deficits lower hormone levels and spontaneous movement, reducing actual expenditure below what static equations predict.

Keep exploring