BMR Calculator
Estimate your basal metabolic rate with the Mifflin-St Jeor and revised Harris-Benedict equations, in metric or imperial units, with every step shown.
Estimate based on published formulas, not medical advice. Talk to a health professional about your situation.
- Mifflin-St Jeor
- – kcal/day
- Harris-Benedict (revised 1984)
- – kcal/day
Mifflin-St Jeor
Harris-Benedict (Roza & Shizgal)
BMR is the energy used at complete rest. To estimate daily needs, multiply it by an activity factor.
How to use the BMR calculator
- Choose Metric (cm, kg) or Imperial (ft, in, lb).
- Select Male or Female and enter your Age (years). The equations were built for adults, so ages from 18 to 100 are accepted.
- Enter your Height and Weight.
- Read your basal metabolic rate from two equations side by side: Mifflin-St Jeor and Harris-Benedict (revised 1984), in kcal/day, with the hourly equivalent. The arithmetic for each equation is listed below the results.
The numbers update as you type and never leave your browser. Clear empties the fields.
What is basal metabolic rate?
Basal metabolic rate (BMR) is the energy your body uses at complete rest to keep you alive: breathing, circulation, temperature control, brain activity and cell repair. It is usually the largest part of daily energy expenditure, often around 60 to 70 % for people who are not very active. Strictly speaking, BMR is measured lying down after a night’s sleep and a 12-hour fast; the closely related resting metabolic rate (RMR) is slightly higher. The equations below were fitted on measured resting values and are used for both.
BMR is not the number of calories you need in a day. To estimate that, multiply it by an activity factor, which is what the TDEE calculator does.
The formulas
Mifflin-St Jeor (Mifflin MD, St Jeor ST et al., American Journal of Clinical Nutrition, 1990;51:241-247), with weight in kg, height in cm and age in years:
- men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
- women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
Harris-Benedict, revised by Roza and Shizgal (American Journal of Clinical Nutrition, 1984;40:168-182), which re-estimated the 1919 equation’s coefficients:
- 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
Worked example: a 30-year-old man weighing 80 kg and measuring 180 cm gets 800 + 1,125 − 150 + 5 = 1,780 kcal/day with Mifflin-St Jeor, and about 1,854 kcal/day with revised Harris-Benedict. Imperial values are converted exactly to kilograms and centimetres before the calculation.
Which equation should you trust?
In a systematic review for the American Dietetic Association (Frankenfield et al., 2005), Mifflin-St Jeor predicted measured resting metabolic rate within 10 % for more people than the other equations tested, including Harris-Benedict, which tends to give slightly higher values. That is why many dietitians use Mifflin-St Jeor by default. Showing both lets you see the range of reasonable estimates.
Limitations
These equations predict an average for people of the same sex, age, height and weight. Your own BMR can differ by 10 % or more because of body composition (muscle burns more energy than fat), genetics, hormones such as thyroid function, medication, illness, pregnancy or breastfeeding. The equations are less reliable for older adults, people with very high or very low body weight, athletes, and anyone with a medical condition. Only indirect calorimetry measures BMR directly.
Use the result as a starting point, not a target, and never as a reason to eat less than your body needs. For a personal nutrition plan, especially with a health condition, consult a doctor or a registered dietitian.
Frequently asked questions
What is a normal BMR?
There is no single normal value: it depends mostly on body size, sex and age. Many adult women fall roughly between 1,200 and 1,500 kcal/day and many adult men between 1,500 and 1,900 kcal/day, but larger or more muscular people are higher.
Why do the two equations give different results?
They were derived from different groups of people measured decades apart. Harris-Benedict data come from the early 20th century; Mifflin-St Jeor used 498 adults measured in the late 1980s, and generally matches modern measurements better.
Should I eat only my BMR in calories?
No. BMR covers only the energy used at rest. Daily needs are higher once digestion and movement are included. Eating at or below BMR for long periods is not recommended without medical supervision.
Why does BMR go down with age?
The age term in both equations reflects the gradual loss of lean mass and small metabolic changes seen on average over the years. Staying active and doing strength training helps maintain muscle.
Can this calculator be used for teenagers?
It is designed for adults. Energy needs of children and teens depend on growth, so ask a paediatrician or dietitian instead.
Related tools
- TDEE and Daily Calorie Calculator Estimate your total daily energy expenditure (TDEE) and maintenance calories from your BMR and activity level, in metric or imperial units.
- Macro Calculator Split your daily calories into protein, carbohydrates and fat. See grams and calories for each macro, compared with the official reference ranges.
- BMI Calculator Calculate your adult body mass index in metric or imperial units, see the WHO BMI category and the weight range for a BMI of 18.5 to 24.9.