BMR Calculator
Calculate your BMR (basal metabolic rate): the calories your body burns at complete rest. Compares the Mifflin-St Jeor and revised Harris-Benedict equations.
💤 BMR Calculator
Basal Metabolic Rate
💡 How the BMR Calculator Works
Your basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive: breathing, circulating blood, maintaining body temperature and keeping your organs working. This calculator estimates it with two established equations from your weight, height, age and sex. For a 30-year-old man of 70 kg and 170 cm, Mifflin-St Jeor gives 1,618 kcal a day and the revised Harris-Benedict equation gives 1,672 kcal a day.
The two BMR equations
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Harris-Benedict, revised by Roza and Shizgal (1984)
Men: BMR = 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age
The original Harris-Benedict equation was published in 1919 from measurements of a few hundred people; the 1984 revision updated its coefficients. Mifflin-St Jeor was developed from a newer, larger sample, and a 2005 systematic review found it the most reliable of the common equations for healthy adults, predicting resting metabolism within 10% of measured values in more people than any other. Use it as your main figure, and treat Harris-Benedict as a comparison.
Worked examples
- Man, 30, 70 kg, 170 cm (Mifflin-St Jeor): 700 + 1,062.5 − 150 + 5 = 1,617.5 kcal.
- Same man (revised Harris-Benedict): 88.362 + 937.79 + 815.83 − 170.31 = 1,671.7 kcal, about 54 kcal higher.
- Woman, 35, 60 kg, 165 cm: Mifflin-St Jeor 1,295 kcal; Harris-Benedict 1,362 kcal.
Mifflin-St Jeor vs Harris-Benedict compared
The two equations give similar results for many adults, with Harris-Benedict usually a little higher. Values in kcal per day:
| Person | Mifflin-St Jeor | Harris-Benedict | Difference |
|---|---|---|---|
| Man, 25, 65 kg, 175 cm | 1,624 | 1,657 | +33 |
| Man, 30, 70 kg, 170 cm | 1,618 | 1,672 | +54 |
| Man, 45, 90 kg, 180 cm | 1,805 | 1,902 | +97 |
| Man, 65, 80 kg, 175 cm | 1,574 | 1,631 | +57 |
| Woman, 25, 55 kg, 160 cm | 1,264 | 1,344 | +80 |
| Woman, 35, 60 kg, 165 cm | 1,295 | 1,362 | +67 |
| Woman, 50, 75 kg, 162 cm | 1,352 | 1,426 | +75 |
| Woman, 65, 65 kg, 158 cm | 1,152 | 1,257 | +105 |
BMR vs RMR vs TDEE
- BMR (basal metabolic rate) is measured under strict conditions: just after waking, after an overnight fast, lying still in a comfortable temperature.
- RMR (resting metabolic rate) is measured under less strict conditions and is usually slightly higher. In everyday use the terms are often interchanged, and the Mifflin-St Jeor equation was actually developed to predict resting energy expenditure.
- TDEE (total daily energy expenditure) adds digestion and all physical activity on top of BMR. Use the TDEE calculator to turn your BMR into daily calorie needs, or the calorie calculator for weight-goal targets.
What affects your BMR
- Lean body mass: muscle and organs use far more energy than fat tissue, so lean mass is the biggest single influence on BMR. This is the main reason men's BMR is usually higher than women's at the same weight.
- Body size: taller and heavier bodies have more tissue to maintain.
- Age: the equations subtract a fixed amount per year (5 kcal in Mifflin-St Jeor). Much of the real-life change with age comes from losing muscle.
- Other factors: genetics, hormones (particularly thyroid hormones), illness and fever, and extreme environments can all shift metabolism. The equations can't account for these.
Does metabolism slow down with age?
Less than many people think. A 2021 study in Science led by Herman Pontzer analysed measurements from more than 6,600 people aged from one week to 95 years across 29 countries. After adjusting for body size, metabolism was most stable from the 20s through the 50s, then declined by about 0.7% a year after 60; people in their 90s needed about 26% fewer calories a day than people in midlife. Keeping or building muscle through strength training helps maintain energy needs as you age.
If you know your body fat percentage
Because lean mass drives BMR, the Katch-McArdle equation uses it directly: BMR = 370 + 21.6 × lean body mass (kg). For a 70 kg man at 17.8% body fat (lean mass 57.5 kg) it gives about 1,613 kcal. This can suit very muscular or very lean people better than weight-based equations. Estimate your body fat with the body fat calculator and lean mass with the lean body mass calculator.
How BMR is measured precisely
Equations are estimates. The accurate method is indirect calorimetry, which measures the oxygen you breathe in and the carbon dioxide you breathe out while resting, and calculates energy use from them. Some clinics, hospitals and sports-science labs offer it.
BMR equations are designed for healthy adults. They are less reliable for children, pregnant women, older adults, people with obesity, highly trained athletes and people with medical conditions that affect metabolism. Use the result as a guide, and speak to a doctor or dietitian for clinical decisions.
Sources
- Mifflin MD, St Jeor ST, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 51(2), 241–247.
- Roza AM, Shizgal HM (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition, 40(1), 168–182.
- Frankenfield D, et al. (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association
- Duke University (2021), reporting Pontzer H, et al., Daily energy expenditure through the human life course, Science