How to use the BMR Calculator
- Select your sex, since the equation uses different constants.
- Enter age, height and weight in the units shown.
- Read the BMR in calories per day.
- Move to the TDEE calculator to add your activity level before setting a diet target.
How the calculation works
The Mifflin-St Jeor equation is used here because it predicts measured resting energy expenditure more accurately than the older Harris-Benedict equation across most adult populations. It weights body mass most heavily, adds a term for height, and subtracts a term for age, reflecting the gradual loss of metabolically active tissue with age.
Because the equation only knows total weight, it cannot see body composition. Two people of the same weight with very different muscle mass have genuinely different resting rates, and for lean, muscular individuals the Katch-McArdle equation — which works from lean body mass — usually fits better. Expect any prediction to sit within roughly 10% of a measured value.
Men: BMR = 10w + 6.25h − 5a + 5 Women: BMR = 10w + 6.25h − 5a − 161 (w kg, h cm, a years)Source: Mifflin MD, St Jeor ST et al., 'A new predictive equation for resting energy expenditure in healthy individuals', Am J Clin Nutr, 1990.
Worked example
A 34-year-old woman, 166 cm tall, weighing 63.5 kg.
- 10 × 63.5 = 635.
- 6.25 × 166 = 1,037.5.
- 5 × 34 = 170.
- 635 + 1,037.5 − 170 − 161 = 1,341.5.
BMR ≈ 1,342 calories per day at complete rest, before any activity is counted.
Frequently asked questions
Is BMR the number of calories I should eat?+
No — eating at BMR would mean fuelling nothing beyond basic organ function. Multiply BMR by an activity factor to get total daily expenditure, and set your intake relative to that.
Why does BMR fall as I lose weight?+
A smaller body costs less to maintain, and some lean tissue is usually lost alongside fat. Recalculate every four to six kilograms of change, otherwise a deficit that worked initially becomes a maintenance intake.
Which equation is best?+
Mifflin-St Jeor for most people. Katch-McArdle is more accurate if you have a reliable body fat measurement, because it works from lean mass rather than total weight.
Can I raise my BMR?+
Modestly, by adding muscle — lean tissue costs more to maintain than fat. The effect is real but small compared with the difference activity levels make to total daily expenditure.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.