BMR Calculator
Find your basal metabolic rate — the calories your body burns at complete rest — using the Mifflin-St Jeor equation dietitians trust most.
The Mifflin-St Jeor equation
Women: BMR = 10×kg + 6.25×cm − 5×age − 161
Man, 30, 178 cm, 75 kg:
10×75 + 6.25×178 − 5×30 + 5 = 750 + 1,112.5 − 150 + 5 = ~1,718 calories/day at rest.
Woman, 45, 5'4" (64 in), 145 lb. Converted: height = 64 × 2.54 = 162.6 cm; weight = 145 × 0.453592 ≈ 65.8 kg.
10×65.8 + 6.25×162.6 − 5×45 − 161 = 658 + 1,016.3 − 225 − 161 = ~1,288 calories/day at rest.
Two things separate this from the male example above: the female formula subtracts 161 instead of adding 5 (a 166-calorie gap by sex alone), and the 15-year age difference (45 vs. 30) subtracts another 75 calories (5 × 15). Together, sex and age account for roughly 241 of the total ~430-calorie gap between the two results — the rest comes from the different height and weight.
What BMR is (and how to use it)
Your BMR is the biggest single piece of your daily calorie burn — the energy to keep your heart beating, lungs working, and cells repairing while you do nothing. It rises with muscle mass and body size, and falls gradually with age. On its own, BMR isn't the number to eat to; multiply it by an activity factor to get your TDEE (maintenance calories), then set a target with the calorie calculator. The activity-adjusted rows above are a shortcut to that TDEE estimate.
Mifflin-St Jeor vs. the older Harris-Benedict equation
| Equation | Introduced | Men's formula |
|---|---|---|
| Harris-Benedict (revised) | 1919 / revised 1984 | 88.362 + 13.397×kg + 4.799×cm − 5.677×age |
| Mifflin-St Jeor | 1990 | 10×kg + 6.25×cm − 5×age + 5 |
For the same person, Harris-Benedict tends to output a slightly higher BMR than Mifflin-St Jeor — for the 178 cm, 75 kg, 30-year-old man in the first example, Harris-Benedict comes out a bit above the ~1,718 calorie Mifflin-St Jeor result. That gap is exactly why most dietitians switched: Mifflin-St Jeor was validated against a more contemporary population and tracks measured resting metabolism more closely on average.
Common mistakes when using BMR
- Eating at or below BMR to lose weight faster. BMR excludes all daily movement, so eating this low creates a far larger deficit than intended and is unsustainable for almost everyone — always plan around TDEE instead.
- Assuming BMR stays constant. BMR declines gradually with age and drops as body weight and muscle mass decrease — recalculating periodically keeps downstream calorie targets accurate.
- Overlooking body composition differences. Two people of the same height, weight, and age can have meaningfully different real BMR if one carries substantially more muscle, since muscle tissue burns more at rest than fat tissue.
- Confusing BMR with a daily calorie target. BMR is a rest-only baseline, not a number to eat to — see the TDEE calculator to translate it into an actual maintenance or goal calorie level.
Frequently asked questions
What is BMR?
Calories burned at complete rest — 60–70% of your total daily burn.
What is the Mifflin-St Jeor formula?
Men: 10×kg + 6.25×cm − 5×age + 5. Women: same but − 161.
BMR vs. TDEE?
BMR is at rest; TDEE multiplies it by activity to give maintenance calories.
Why does BMR decrease with age?
Aging is typically associated with gradual loss of muscle mass and a slight decline in organ metabolic activity, both of which lower the calories burned at rest even when body weight stays the same.
Does more muscle mean a higher BMR?
Yes. Muscle tissue is more metabolically active than fat tissue, so a more muscular person generally has a higher BMR than a less muscular person of the same height, weight, age, and sex.
How does this compare to the Harris-Benedict equation?
Harris-Benedict tends to run a bit higher for the same inputs. Most dietitians now prefer Mifflin-St Jeor since it was validated against a more contemporary population.
How much does a 15-year age difference change BMR?
About 75 calories under Mifflin-St Jeor, since each year subtracts 5 calories — before any change in weight, height, or sex.
Related calculators
Medical disclaimer: BMR is an estimate for healthy adults and varies with body composition and genetics. Not medical advice. Consult a healthcare provider or dietitian for personalized guidance. Formula: Mifflin-St Jeor (1990). Last reviewed: September 2026.