Your basal metabolic rate (BMR) is the number of calories your body burns at complete rest, just to keep you alive: breathing, circulating blood, maintaining body temperature and repairing cells. This calculator estimates your BMR with the Mifflin-St Jeor equation, then shows how many calories you're likely to burn in a day at different activity levels.
How to use the BMR calculator
- Choose metric or imperial units.
- Select male or female, since the equation differs slightly between the two.
- Enter your age, height and weight.
- Read your BMR in kilocalories (kcal) per day.
- Look at the activity table to estimate your total daily calorie use.
The Mifflin-St Jeor equation
The calculator uses the equation published by Mifflin, St Jeor and colleagues in 1990. With weight in kilograms, height in centimetres and age in years:
- Men: BMR = 10 × weight + 6.25 × height − 5 × age + 5
- Women: BMR = 10 × weight + 6.25 × height − 5 × age − 161
Imperial inputs are converted to kilograms and centimetres first.
A 2005 review of the common prediction equations by the American Dietetic Association found Mifflin-St Jeor the most reliable for healthy adults. It came within 10% of measured resting energy use for most people, but it was less accurate for people with obesity.
Worked examples
A 30-year-old woman, 165 cm tall, weighing 60 kg:
- 10 × 60 = 600
- 6.25 × 165 = 1,031.25
- 5 × 30 = 150
- BMR = 600 + 1,031.25 − 150 − 161 = about 1,320 kcal per day
A 35-year-old man, 180 cm tall, weighing 80 kg:
- 10 × 80 = 800
- 6.25 × 180 = 1,125
- 5 × 35 = 175
- BMR = 800 + 1,125 − 175 + 5 = 1,755 kcal per day
From BMR to daily calories (TDEE)
Your BMR is only the resting part of the calories you use. Your total daily energy expenditure (TDEE) adds everything else: walking, working, exercising and digesting food. The calculator estimates TDEE by multiplying your BMR by an activity factor:
| Activity level | Description | Multiply BMR by |
|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.2 |
| Lightly active | Light exercise 1 to 3 days a week | 1.375 |
| Moderately active | Moderate exercise 3 to 5 days a week | 1.55 |
| Very active | Hard exercise 6 to 7 days a week | 1.725 |
For the woman in the example above, lightly active: 1,320 × 1.375 = about 1,815 kcal a day. For the man, moderately active: 1,755 × 1.55 = about 2,720 kcal a day.
Most people overestimate how active they are. If you're unsure, start with the lower level and adjust based on how your weight actually changes over a few weeks.
Why BMR differs between people
- Body size. Larger bodies have more tissue to maintain, so BMR rises with weight and height.
- Muscle. Muscle uses more energy at rest than fat. Two people with the same weight can differ noticeably if one is more muscular.
- Age. BMR tends to fall with age, partly because muscle mass declines. The equation subtracts 5 kcal for each year.
- Sex. Men usually have more muscle and less fat at the same weight, which the equation reflects in its constants.
- Other factors. Thyroid conditions, some medications, pregnancy, breastfeeding and illness can change BMR in ways no equation can predict.
Limits of any BMR calculator
The equation estimates an average for people like you; it doesn't measure you. Your real BMR may be a few hundred calories higher or lower. Indirect calorimetry, which measures the oxygen you breathe in and the carbon dioxide you breathe out, is the only way to measure it directly, and it's usually available only in clinics and research settings.
The equation was developed for adults. It isn't suitable for children, and it's less reliable for very muscular people, people with obesity, and people with medical conditions that affect metabolism. If you're planning significant changes to how you eat, especially with a health condition, talk to a doctor or registered dietitian.
BMR calculator FAQ
What's the difference between BMR and RMR?
BMR is measured under strict conditions: fully rested, fasted, and at a comfortable temperature. Resting metabolic rate (RMR) is measured under less strict conditions and is usually slightly higher. In everyday use the two terms are often used interchangeably, and prediction equations like this one estimate roughly the same thing.
Is Mifflin-St Jeor better than Harris-Benedict?
For most healthy adults, research has found Mifflin-St Jeor to be more accurate than the older Harris-Benedict equation, which was first published in 1919 and tends to overestimate. That's why most dietitians now use Mifflin-St Jeor.
How many calories should I eat to lose weight?
Eating fewer calories than your TDEE leads to weight loss over time, but how large a deficit is safe and sustainable depends on your health, age and starting point. A doctor or registered dietitian can give advice that fits you. This calculator only estimates how much energy you use.
Why is my BMR lower than I expected?
BMR covers only what your body burns at complete rest, and it's usually well below the total you burn in a day. Check the activity table for a figure closer to your real daily use.
Is my information stored?
No. The calculation happens in your browser, and nothing you enter is sent anywhere.