How to use the BMR calculator
- Choose Metric (cm, kg) or US units (ft, in, lb).
- Pick your sex and enter your age (18 or over).
- Enter your height and weight.
- Optionally enter your body fat percentage. It's needed only for the Katch-McArdle equation.
- Choose the equation for the main result. The table shows all three.
How BMR is calculated
Basal metabolic rate (BMR) is the energy your body needs to stay alive at rest: breathing, circulation, keeping warm and repairing cells. It accounts for roughly 60–70% of the calories most people burn in a day. The calculator offers three equations (weight in kg, height in cm, age in years):
Mifflin-St Jeor is the default because reviews have found it the most accurate of the common equations for healthy adults. Harris-Benedict dates from 1919, and the 1984 revision is still widely used, though it tends to run a little high. Katch-McArdle ignores age and sex and uses lean mass instead. That makes it a better choice for very muscular people, but only if your body fat figure is reliable.
Worked example
These are the calculator's defaults: a 35-year-old man, 175 cm, 70 kg.
- Mifflin-St Jeor: 10 × 70 + 6.25 × 175 − 5 × 35 + 5 = 700 + 1,093.75 − 175 + 5 = 1,624 kcal a day (6,795 kJ)
- Revised Harris-Benedict: 13.397 × 70 + 4.799 × 175 − 5.677 × 35 + 88.362 = 937.79 + 839.83 − 198.70 + 88.36 = 1,667 kcal
- Katch-McArdle with 18% body fat: lean mass = 70 × 0.82 = 57.4 kg, so BMR = 370 + 21.6 × 57.4 = 1,610 kcal
The three land within about 60 kcal of each other here. For people of average build, that's typical.
What changes your BMR
| Factor | Effect |
|---|---|
| More muscle | Raises BMR; muscle burns more energy at rest than fat |
| Age | BMR falls slowly through adulthood, mostly as muscle is lost |
| Sex | Men usually have higher BMR at the same size, mainly from more lean mass |
| Weight loss | BMR falls as you get lighter, and can drop a little more than expected |
| Thyroid hormone | An overactive thyroid raises BMR; an underactive one lowers it |
| Illness and fever | Can raise needs temporarily |
To turn BMR into the calories you need in a day, multiply it by an activity factor. The TDEE calculator does this for every activity level, and the calorie calculator adds targets for losing or gaining weight.
Limits of the equations
All three are estimates built from groups of people, and an individual can be 10% or more away from the result. They are less reliable for people with obesity, older adults, athletes, and anyone who is ill. They aren't meant for children or for pregnancy. If you need an exact figure, for example for medical nutrition support, a dietitian can arrange a measurement by indirect calorimetry. Talk to your doctor if you suspect a thyroid or other metabolic problem.
Frequently asked questions
What is the difference between BMR and RMR?
BMR is measured under strict conditions: after a night's sleep, fasting and fully at rest. Resting metabolic rate (RMR) is measured under looser conditions and usually comes out slightly higher. The equations here are often used for both, and the difference is small.
Should I eat only my BMR in calories?
No. BMR covers only the energy you'd use lying still all day. Eating at or below BMR for long periods makes it hard to get enough nutrients. Use your total daily energy expenditure as the starting point instead, and talk to a dietitian before trying a very low intake.
Which BMR equation should I use?
For most adults, Mifflin-St Jeor. If you know your body fat percentage from a reliable measurement and you're quite muscular, Katch-McArdle may suit you better. Harris-Benedict is included for comparison, since many older apps and charts use it.
Why is my BMR lower than my friend's?
Body size and composition matter most. A taller or heavier person, or one with more muscle, burns more at rest. Age and sex play a smaller part. Differences of a few hundred calories between people of different sizes are normal.
Related calculators
- TDEE Calculator — Total daily energy expenditure: your BMR multiplied by your activity level, with every level side by side.
- Calorie Calculator — Daily calories to maintain your weight, plus gradual targets for losing or gaining, using the Mifflin-St Jeor equation.
- Lean Body Mass Calculator — Lean body mass from your height and weight with the Boer, James and Hume formulas, plus the body fat each implies.
- Body Fat Calculator — Estimate your body fat percentage with the U.S. Navy tape method and compare it with a BMI-based estimate.
Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.