What BMR is
Your basal metabolic rate is the energy your body uses in a day just to stay alive at rest: breathing, circulation, keeping warm and running your organs. For most people it is 60–70% of daily calorie burn. Activity and digesting food make up the rest; to estimate your total daily needs, use the calorie calculator, which multiplies BMR by an activity factor.
Equations
- Mifflin–St Jeor (1990): 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for men or −161 for women. It is the equation most dietitians use today.
- Harris–Benedict (revised 1984): an older equation that tends to give slightly higher values.
Worked example
A 30-year-old woman, 165 cm (5 ft 5 in) and 60 kg (132 lb): 600 + 1,031.25 − 150 − 161 = 1,320 kcal a day by Mifflin–St Jeor. Harris–Benedict gives 1,384 kcal.
Accuracy
Even the best equation can be off by 10% or more for an individual, because body composition matters: muscle burns more energy than fat. Treat the result as a starting point and adjust based on how your weight actually changes.
How this works
The page converts US inputs to kilograms and centimeters, then applies the Mifflin–St Jeor equation for the headline and the revised Harris–Benedict equation for comparison. Both are rounded to whole calories, and the Mifflin value is also shown in kilojoules (1 kcal = 4.184 kJ). Everything is calculated in your browser.
Frequently asked
What is the Mifflin–St Jeor equation?
10 × kg + 6.25 × cm − 5 × age, plus 5 for men or minus 161 for women.
Is BMR the same as calories burned in a day?
No. BMR is at rest; total daily energy expenditure adds activity and digestion, typically 1.2 to 1.9 times BMR.
Why do the two equations differ?
They were fitted on different study groups decades apart. Mifflin–St Jeor matches modern measurements better.
Should I eat less than my BMR to lose weight?
Generally no. Aim for a moderate deficit from your total daily needs, and get professional advice for large changes.
Sources
- Mifflin et al. (1990) — A new predictive equation for resting energy expenditure in healthy individuals, Am J Clin Nutr
- Roza & Shizgal (1984) — The Harris Benedict equation reevaluated, Am J Clin Nutr
- Wikipedia — Basal metabolic rate
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/health/bmr-calculator/