BMR Calculator
Your baseline daily calorie burn — the Mifflin-St Jeor estimate, explained.
Free · No sign-up · Runs locally in your browser · Also available in Chinese (中文)
What is BMR Calculator?
A BMR calculator estimates Basal Metabolic Rate: the energy your body spends just existing for a day — brain, heart, breathing, cell repair — before any movement. The standard Mifflin-St Jeor equation uses weight, height, age and sex, and is what most modern nutrition references cite.
BMR is the anchor of every calorie plan: total daily burn is roughly BMR × activity factor. Knowing your baseline turns vague advice like 'eat less' into an actual number you can plan meals around — and explains why crash diets below BMR feel awful and rarely last.
How to use it
- 1Enter your sex, age, height and current weight.
- 2Read the BMR estimate in calories per day.
- 3Multiply by an activity factor (1.2 sedentary to 1.9 very active) for total daily needs.
- 4Plan intake relative to that total for maintain, lose or gain goals.
Common use cases
- Setting a realistic calorie target with a coach or dietitian.
- Understanding why two people of different sizes need different portions.
- Tracking how muscle gain raises your baseline over a training cycle.
Frequently asked questions
▸How accurate is the estimate?
Mifflin-St Jeor is accurate within roughly 10% for most adults. Lab measured values (indirect calorimetry) beat any formula, but this is the best you can get from a calculator.
▸Does more muscle raise BMR?
Yes — muscle is metabolically active tissue. It is a modest effect per pound, but meaningful over months of training and one reason strength work supports weight management.