BMR Calculator
Basal Metabolic Rate (Mifflin-St Jeor)
This free BMR Calculator works out your Basal Metabolic Rate — the number of calories your body burns in twenty four hours doing absolutely nothing but staying alive — using the Mifflin-St Jeor equation, the formula most often recommended for general use. Enter your sex, age, weight and height and you get your BMR, plus a ready-made table showing how that resting figure grows into total daily calorie needs at five standard activity levels, from sedentary desk work right up to very physical jobs and hard daily training.
BMR is the foundation of almost every sensible diet and nutrition plan, because eating below it for long is generally unwise and eating around the activity-adjusted figure keeps weight stable. Still, treat the result as an estimate only, not medical advice: two people with identical stats can have genuinely different metabolic rates because of muscle mass, thyroid function, medication and other factors a four-question formula cannot see. Anyone pregnant, breastfeeding, under eighteen or managing a health condition should get personal guidance from a doctor or dietitian. The calculation runs entirely in your browser, so your details never leave your device.
How to use
- Select your sex and type your age in years.
- Enter your weight in kilograms and height in centimetres.
- Click Calculate BMR to see your resting calorie burn.
- Find your activity level in the table below the result.
- Read across to see the calories that roughly maintain your weight.
Frequently asked questions
Why do men and women get different constants?
The Mifflin-St Jeor equation adds five for men and subtracts one hundred and sixty one for women. This reflects average differences in body composition between the sexes at the same weight and height, particularly typical muscle and fat proportions.
Can I eat below my BMR to lose weight faster?
It is generally not recommended without medical supervision. BMR covers only basic life functions, and sustained eating below it can cost energy, mood and muscle. A modest deficit below your maintenance calories is the approach most guidelines favour.
Does BMR change as I lose or gain weight?
Yes. A lighter body burns fewer calories at rest, which is one reason weight loss slows over time. Recalculate whenever your weight changes by several kilograms so your targets keep matching your current body.
How is BMR different from RMR?
Resting Metabolic Rate is measured under slightly looser conditions and usually comes out a little higher. In everyday planning the two are used almost interchangeably, and this calculator follows the standard BMR formula used by most nutrition tools.