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Your Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest just to keep you alive. It powers your heartbeat, breathing, brain, and the constant repair happening inside your cells, and it is the single largest part of your daily calorie burn.
What is BMR?
Even if you spent the whole day lying still, your body would burn a substantial amount of energy. That baseline is your BMR. For most people it accounts for 60 to 70 percent of total daily calories, which is why it is the foundation of any nutrition plan.
How BMR is calculated
The Mifflin-St Jeor equation estimates BMR from your weight, height, age, and sex. It is the modern standard and the most accurate for the general population. This tool also shows the older Harris-Benedict result so you can compare the two.
What affects your BMR
- Muscle mass: muscle burns more at rest than fat, so more lean mass means a higher BMR.
- Age: BMR gradually declines with age, partly due to muscle loss.
- Sex: men usually have a higher BMR because they tend to carry more muscle.
- Body size: larger bodies need more energy to maintain.
Turning BMR into calorie needs
BMR alone is not what you should eat. To get the calories you actually need, multiply your BMR by an activity factor to reach your Total Daily Energy Expenditure, then adjust for your goal. Our TDEE and calorie calculators do that next step, and SmaartCoach builds the meals to match.
Frequently asked questions
What is BMR?
Basal Metabolic Rate is the number of calories your body burns just to keep you alive at rest: breathing, circulation, and cell repair. It is usually 60 to 70 percent of the calories you burn each day.
BMR vs TDEE, what is the difference?
BMR is your at-rest burn. TDEE is BMR plus everything else you do: moving, digesting, and exercising. You eat around your TDEE, not your BMR.
Which BMR formula is best?
The Mifflin-St Jeor equation is considered the most accurate for the general population, which is why we show it as the primary result.
Can I increase my BMR?
Building muscle raises your resting burn because muscle is more metabolically active than fat. Strength training and enough protein are the reliable levers.
Sources
Reviewed against these authoritative references. Last updated August 2026.
- MedlinePlus, U.S. National Library of Medicine. Metabolism
- MedlinePlus, U.S. National Library of Medicine. Body Weight
- U.S. Department of Health and Human Services. Physical Activity Guidelines for Americans
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