BMR Calculator
Work out your basal metabolic rate, the calories your body burns at complete rest.
Runs in your browser — nothing is sent or saved.
How to work out your BMR
- Choose your sex and enter your age.
- Pick metric or imperial, then enter your height and weight.
- Leave the formula on Mifflin-St Jeor, or switch it.
- Read your basal metabolic rate in calories per day.
What basal metabolic rate means
Your basal metabolic rate is the energy your body uses just to stay alive at complete rest: breathing, circulating blood, keeping your organs and brain running. It is often the largest share of the calories you burn in a day, before any movement is added. Knowing your BMR is the first step to setting a sensible calorie target, which is why the BMR formula sits under most diet plans.
The three formulas
This tool offers three well-known equations so you can compare them.
| Formula | Notes |
|---|---|
| Mifflin-St Jeor | Published 1990, the modern default, closest to measured resting metabolic rate for most people |
| Revised Harris-Benedict | The 1984 update of the classic 1919 equation, tends to read slightly higher |
| Katch-McArdle | Uses lean body mass from your body-fat %, so it suits lean or very muscular people |
Mifflin-St Jeor for a man is 10 times weight in kg, plus 6.25 times height in cm, minus 5 times age, plus 5. For a woman the last term is minus 161 instead. The Katch-McArdle option asks for your body-fat percentage because it is built on lean mass, not total weight.
Sources: Mifflin MD, St Jeor ST, et al., American Journal of Clinical Nutrition (1990); Roza AM, Shizgal HM, revised Harris-Benedict (1984); Katch and McArdle.
BMR is not your daily need
BMR is resting energy only. Your real daily need, the total daily energy expenditure or TDEE, is BMR multiplied by an activity factor between about 1.2 and 1.9. So how many calories at rest is only part of the picture. Use the TDEE calculator to add your activity and get the number you would actually eat to.
An estimate, not medical advice
These equations are population averages, so your true resting metabolic rate can differ by a few hundred calories. Illness, thyroid conditions, and body composition all shift it. Treat the result as a guide and see a doctor or dietitian for anything health-related.
FAQ
What is a normal BMR?
It depends on size, age, and sex, but many adults fall somewhere between roughly 1,300 and 1,900 calories a day at rest. Larger and younger people tend to be higher.
Which BMR formula is most accurate?
For most people Mifflin-St Jeor is the closest to measured resting metabolic rate, which is why dietitians favour it. Katch-McArdle can be better if you know your body-fat %.
What is the difference between BMR and TDEE?
BMR is the calories you burn at rest. TDEE is BMR times an activity multiplier, so it includes daily movement and exercise. TDEE is the number you eat to.
Does BMR change over time?
Yes. It usually falls slowly with age and with loss of muscle, and it rises with more lean mass. That is why the numbers shift as you do.
Are my details private?
Yes. The calculation runs in your browser and nothing you enter is uploaded or saved.