BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to stay alive — powering your organs, breathing, circulation, and body temperature. It's roughly 60–70% of the calories you burn each day and forms the base of your TDEE. You estimate it with the Mifflin-St Jeor formula from your age, weight, height, and sex.
Calculate your BMR
See your BMR across three formulas side by side, plus your burn at every activity level. Free, no signup.
What BMR is
If you stayed in bed all day, doing absolutely nothing, you'd still burn a large number of calories — keeping your heart beating, your lungs working, your brain running, and your body warm. That baseline is your basal metabolic rate. For most people it's 1,200–1,800 calories a day, and it's the single biggest component of how much you burn.
The three main BMR formulas
Mifflin-St Jeor (most accurate for most people)
Revised Harris-Benedict (older, still common)
Katch-McArdle (best if you know body fat %)
The BMR Calculator runs all three at once so you can compare — handy because Mifflin and Harris-Benedict can differ by 50–100 kcal, and Katch-McArdle pulls ahead once you have a body fat figure.
What affects your BMR
- Muscle mass — the biggest lever you control. Muscle is metabolically active, so more lean mass means a higher BMR. This is why resistance training helps long-term.
- Body size — bigger bodies burn more at rest.
- Age — BMR gradually declines with age, largely due to muscle loss.
- Sex — men typically have higher BMR due to more lean mass on average.
- Severe dieting — very low intakes can lower BMR (adaptive thermogenesis) as the body conserves energy.
BMR vs TDEE
These two get confused constantly. BMR is rest only. TDEE is everything. You never eat at your BMR — that's the floor — you eat relative to your TDEE, which adds digestion, daily movement, and exercise on top. To go from one to the other, multiply BMR by an activity factor. Full breakdown in what is TDEE.
Why your BMR matters
BMR is the starting point for every calorie target. Once you know it, you calculate your TDEE, then adjust for your goal. It also tells you your safe lower limit, and it explains why building muscle quietly raises how much you can eat. Calculate it once, recheck it after a significant change in weight or training, and build everything else on top.
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BMR (Basal Metabolic Rate) is the calories your body burns at complete rest to keep you alive. It's roughly 60–70% of your total daily burn and the foundation of your TDEE. Calculate yours with the free BMR Calculator.
The most used formula is Mifflin-St Jeor: men, (10 × kg) + (6.25 × cm) − (5 × age) + 5; women, the same but − 161. Katch-McArdle is more accurate if you know your body fat percentage, as it's based on lean body mass.
BMR is the calories you burn at rest. TDEE is BMR plus digestion, daily movement, and exercise. TDEE is always higher and is what you base your eating on; BMR is the building block. See what is TDEE.
Yes, modestly — mainly by building muscle through resistance training, since muscle burns more at rest than fat. Staying well-fed (avoiding chronic crash diets) and staying active also help keep BMR from dropping. There's no supplement or "metabolism booster" that meaningfully raises it.