Formula, in Fat Loss
BMR Formula (Mifflin-St Jeor)
BMR is the calories you'd burn lying still all day. The Mifflin-St Jeor equation has been the most accurate population estimate since 1990. Note the sex constant: +5 for males, −161 for females — a 166-calorie/day difference baked into the formula.
5 variables. Published Mar 12, 2026. Updated May 10, 2026. By AI Fit Hub.
BMR = 10·mass_kg + 6.25·height_cm − 5·age + s
where s = +5 (male) or −161 (female) Variables
BMR
Basal Metabolic Rate
Calories burned per 24 h at complete rest in a thermoneutral environment. Roughly 60–75% of total daily energy expenditure for sedentary adults.
mass_kg
Body mass
Kilograms. Lean mass drives most of the metabolic rate; this equation uses total mass as a practical proxy.
height_cm
Height
Centimeters. Taller people have larger organ mass and skin surface area, which lifts baseline burn.
age
Age
Years. BMR declines about 1–2% per decade after 20 as lean mass falls and mitochondrial efficiency drops.
s
Sex constant
+5 for males, −161 for females. Reflects average lean-mass and organ-size differences observed in the 1990 Mifflin-St Jeor sample (n=498).
Step by step
- 1
Multiply body mass in kilograms by 10.
78 kg × 10 = 780 cal.
- 2
Multiply height in centimeters by 6.25 and add.
178 cm × 6.25 = 1,112.5 cal. Running total: 1,892.5.
- 3
Multiply age by 5 and subtract.
30 yr × 5 = 150 cal. Running total: 1,742.5.
- 4
Apply the sex constant: add 5 for males, subtract 161 for females.
Male: +5 → 1,747.5 BMR. Female with the same height/weight/age would land at 1,581.5 BMR.
Worked example
30-year-old male, 78 kg, 178 cm
Sex
Male
Age
30
Weight (kg)
78
Height (cm)
178
BMR = 10·78 + 6.25·178 − 5·30 + 5 = 780 + 1,112.5 − 150 + 5 = 1,747.5 calories/day
Baseline burn 1,747.5 cal/day. Multiply by activity factor (1.2 sedentary → 1.9 athlete) to estimate total daily expenditure.
Common variations
Run the numbers next
- Nutrition TDEE Calculator
Estimate your daily energy expenditure with Mifflin-St Jeor + activity factors.
- Planning Calorie Deficit Calculator
Estimate required daily calorie deficit for a target timeline and bodyweight change.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals , American Journal of Clinical Nutrition (Mifflin et al., 1990)
- Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults , Journal of the American Dietetic Association (2005)