BMR (Mifflin-St Jeor) Formula
Estimate basal metabolic rate — the calories your body burns at rest.
BMR = 10·w + 6.25·h − 5·a + s (s = +5 male, −161 female)
How it works
Basal metabolic rate is what the body spends doing nothing at all — running the heart, brain, kidneys and basic cellular maintenance — and it accounts for roughly 60 to 75% of daily energy use in most people. It is not the number to eat to. Total daily expenditure is BMR multiplied by an activity factor, conventionally 1.2 for sedentary, about 1.375 lightly active, 1.55 moderately active, 1.725 very active and up to 1.9 for hard physical work or heavy training. A 70 kg, 175 cm, 30-year-old man has a BMR of about 1,649 kcal/day, which is roughly 1,978 kcal sedentary or 2,556 kcal moderately active. Mifflin-St Jeor dates from 1990 and replaced the older Harris-Benedict equation because it estimates modern populations more accurately, but it is still a regression fitted to a sample rather than a measurement of you. Expect it to be within about 10% for most people and further out at the extremes. Its main blind spot is body composition: it uses total weight and cannot tell muscle from fat, so it tends to under-estimate a lean, muscular person and over-estimate someone carrying more fat at the same weight. If you know your body-fat percentage, the Katch-McArdle formula uses lean mass instead and is usually closer.
Variables
- wWeight in kg
- hHeight in cm
- aAge in years
- sSex offset (+5 male, −161 female)
Worked examples
| Input | Result |
|---|---|
| 70 kg, 175 cm, 30 yr, M | 10·70 + 6.25·175 − 5·30 + 5 ≈ 1,649 kcal/day |
| 60 kg, 165 cm, 30 yr, F | 10·60 + 6.25·165 − 5·30 − 161 ≈ 1,320 kcal/day |
Practical applications
- Setting a starting calorie target before adjusting it against real weight change
- Estimating a deficit or surplus for weight loss or gain
- Planning macronutrient splits once the calorie total is fixed
- Comparing energy needs across ages, since the equation subtracts 5 kcal per year
Common mistakes
- Entering pounds and inches. The equation expects kilograms and centimetres; 175 cm, not 1.75 m and not 69 inches.
- Eating to BMR rather than to total daily expenditure. BMR is the resting figure only.
- Forgetting the sex offset, which is +5 for men and −161 for women — a difference of 166 kcal.
- Treating the output as measured rather than estimated. It is a population regression, typically within about 10%.
- Expecting it to account for muscle. At equal weight it cannot distinguish body composition; Katch-McArdle can.
Used in
Use it in a tool
FAQs
Why Mifflin-St Jeor over Harris-Benedict?+
Mifflin-St Jeor (1990) was re-fit on modern body compositions and is ~5% more accurate for today's population.
Is BMR the same as TDEE?+
No — TDEE = BMR × activity factor (1.2 sedentary up to 1.9 highly active).