Health & Wellbeing
Basal Metabolic Rate (BMR)
Calories your body burns at complete rest.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
Basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive — running the heart, brain, kidneys, liver and the work of breathing and staying warm. It is the largest single part of most people's daily energy use, typically around 60-70% of the total. This calculator uses the Mifflin-St Jeor equation: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5 for men, or - 161 for women. It was published in 1990 and derived in healthy adults, and it generally predicts resting energy expenditure more closely than the older Harris-Benedict equation.
Interpreting the result
The result is an estimate of the calories you would burn over 24 hours doing nothing at all. It is not a target to eat to — almost nobody spends the day at complete rest, so your actual daily need is higher. To get from BMR to a realistic daily figure, multiply by an activity factor (the Daily Calorie Needs calculator does this for you). Expect the estimate to be within roughly 10% of a measured value for most healthy adults, and less accurate at the extremes of body composition.
Advice
This is the energy used just to keep your body working at rest. Your total daily needs are higher once activity is added — see the Daily Calorie Needs calculator.
Worked example
A 35-year-old man, 82 kg and 178 cm: (10 x 82) + (6.25 x 178) - (5 x 35) + 5 = 820 + 1112.5 - 175 + 5 = 1762 kcal/day. That is his resting requirement. If he is moderately active, his total daily need would be roughly 1762 x 1.55, about 2730 kcal.
Pearls / pitfalls
- BMR falls with age and with weight loss — the equation captures the age term, but after significant weight loss measured metabolic rate is often a little lower than predicted.
- It was derived in healthy adults. Treat it with caution in pregnancy, in serious illness, in people with very high muscle mass, and in children, where it was not validated.
- Sex enters the equation as a flat offset (+5 or -161 kcal), which is a simplification of real differences in body composition rather than a biological constant.
- BMR and RMR (resting metabolic rate) are used interchangeably in most everyday contexts, though strictly BMR is measured under stricter fasting and rest conditions and comes out slightly lower.
Evidence & validation
The Mifflin-St Jeor equation was derived and cross-validated in healthy adults by Mifflin and colleagues (1990) and has since been widely adopted in dietetic practice, where reviews have generally found it to predict resting metabolic rate in non-obese and obese adults more accurately than Harris-Benedict. It remains a prediction equation, not a measurement: indirect calorimetry is the reference standard.
Frequently asked questions
Should I eat my BMR number of calories?
No. BMR is what you would burn at complete rest, so eating only that amount would put most people in a substantial deficit. Use your total daily energy expenditure — BMR multiplied by an activity factor — as the maintenance figure.
Why is the male and female result so different?
The equation adds 5 kcal for men and subtracts 161 kcal for women, reflecting average differences in lean tissue at the same height and weight. It is an average adjustment and will not fit every individual.
Is Mifflin-St Jeor better than Harris-Benedict?
For most healthy adults, yes — it was developed later on a more representative sample and generally predicts resting energy expenditure more closely. Both are estimates rather than measurements.
How accurate is the estimate?
For most healthy adults it lands within about 10% of a measured value. Accuracy falls at the extremes — very muscular, very lean, very elderly or acutely unwell people.
Does exercise change my BMR?
Exercise adds to your total daily energy use directly. It can also raise BMR slightly over time by increasing muscle mass, but the effect is modest compared with the calories burned during the activity itself.
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247.
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