Free body composition & weight tool
BMR Calculator
Basal metabolic rate (BMR) is the energy your body uses at rest in a day. The Mifflin-St Jeor equation estimates it as 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5 for men or − 161 for women. A 35-year-old woman who is 5 ft 7 in and 165 lb comes out near 1,476 kcal/day. The calculator also shows revised Harris-Benedict and Katch-McArdle.
Prepared by Prospyr · Reviewed October 3, 2026 · Free, no sign-up, runs in your browser
Only needed for Katch-McArdle. Leave blank if you do not have a measured value.
Basal metabolic rate (Mifflin-St Jeor)
1,476kcal/day
Estimated calories your body uses at rest in 24 hours. About 62 kcal per hour.
Harris-Benedict (revised)
1,515 kcal
+39 vs Mifflin
Katch-McArdle
Add body fat %
Estimates from published equations; individual resting energy varies. This is not medical or dietary advice. For a daily calorie estimate, use the TDEE calculator.
BMR formulas: Mifflin-St Jeor, Harris-Benedict and Katch-McArdle
All three are shown together so you can see the spread. Weight is in kg, height in cm and age in years.
| Equation | Women | Men |
|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A − 161 | 10W + 6.25H − 5A + 5 |
| Harris-Benedict, revised (1984) | 447.593 + 9.247W + 3.098H − 4.330A | 88.362 + 13.397W + 4.799H − 5.677A |
| Katch-McArdle | 370 + 21.6 × lean body mass (kg), same for both sexes | |
Mifflin-St Jeor is the default. Harris-Benedict is the older equation, as revised by Roza and Shizgal in 1984. Katch-McArdle needs a body fat percentage because it uses lean mass: weight × (1 − body fat ÷ 100).
Worked example
A 35-year-old woman, 5 ft 7 in (170.2 cm) and 165 lb (74.8 kg):
- Mifflin-St Jeor: 10 × 74.84 + 6.25 × 170.18 − 5 × 35 − 161 = 748.4 + 1,063.6 − 175 − 161 = 1,476 kcal/day
- Harris-Benedict (revised): 447.593 + 9.247 × 74.84 + 3.098 × 170.18 − 4.33 × 35 = 1,515 kcal/day
For a 30-year-old man at 80 kg, 180 cm and 20% body fat: Mifflin-St Jeor gives 1,780, revised Harris-Benedict 1,854, and Katch-McArdle (lean mass 64 kg) 370 + 21.6 × 64 = 1,752 kcal/day. Differences of 50 to 100 kcal between equations are normal.
BMR calculator for women and men: what changes
Women's results come out lower in Mifflin-St Jeor by 166 kcal at the same weight, height and age, because the constant is −161 instead of +5. In practice, body size and lean mass explain most of the difference between people, which is why Katch-McArdle can be useful when you have a body composition measurement.
None of these equations account for pregnancy, thyroid conditions, medications or illness. Results for people far outside the age range studied (Mifflin-St Jeor: 19 to 78 years) are less reliable.
From BMR to daily calories
BMR is the floor, not what a person eats. Daily energy use adds movement and exercise on top. Take your result to the TDEE calculator for maintenance calories, and see the protein intake calculator for protein ranges. Practices that run weight programs can keep these measurements with the rest of the patient record in Prospyr charting.
Frequently asked questions
What is BMR?
BMR, or basal metabolic rate, is an estimate of the calories your body uses at rest to keep breathing, circulating blood and running organs. Equations estimate it from weight, height, age and sex. Lab measurement by indirect calorimetry is the reference method, and the equations are fitted to it.
What is the Mifflin-St Jeor equation?
It is a resting energy equation published in 1990 from 498 healthy adults: REE = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5 for men, or − 161 for women. The authors found the 1919 Harris-Benedict equations overestimated measured energy use by 5% in their sample.
BMR calculator for women: is the formula different?
Only the constant differs. Mifflin-St Jeor subtracts 161 for women and adds 5 for men, with the same weight, height and age terms. Revised Harris-Benedict and Katch-McArdle also differ: Harris-Benedict has separate coefficients by sex, and Katch-McArdle uses lean mass only.
Which BMR equation is the most accurate?
A systematic review of predictive equations in healthy non-obese and obese adults (Frankenfield 2005) found Mifflin-St Jeor most likely to estimate resting metabolic rate within 10% of measured. No equation is right for everyone, so treat every result as an estimate.
When should I use Katch-McArdle?
Use it when you have a measured body fat percentage, because it works from lean mass: 370 + 21.6 × lean body mass in kg. The result is only as good as the body fat number, and body fat estimates from scales and calipers can be off by several points.
What is the difference between BMR and RMR?
BMR is measured under strict conditions: awake, fasted and rested. Resting metabolic rate (RMR) is measured under looser conditions and runs slightly higher. The equations here are fitted to resting energy expenditure, so the terms are used interchangeably in most online calculators.
How do I turn BMR into daily calories?
Multiply BMR by an activity factor to get total daily energy expenditure. The TDEE calculator does this for you and shows a calorie deficit table.
Sources and scope
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 1990;51:241-247 (PubMed 2305711)
Peer-reviewed. The Mifflin-St Jeor equation, derived from 498 healthy adults aged 19 to 78, and the 5% overestimate by Harris-Benedict in that sample.
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr 1984;40:168-182 (PubMed 6741850)
Peer-reviewed. Source of the revised Harris-Benedict coefficients used here.
- Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005 (PubMed 15883556)
Peer-reviewed systematic review comparing equations against measured resting metabolic rate.
- Tang M, et al. Metabolic adaptation fluctuates with different prediction equations. Front Nutr 2025;12 (PMC12425712)
Peer-reviewed trial analysis that prints the Katch-McArdle equation used here: RMR = 370 + 21.6 × lean body mass (kg).
Estimates from published equations, for general information. They are not medical or dietary advice and do not replace measurement or guidance from a clinician.