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BMR formula
All three are respected; pick one or compare them below.
Your results
Formula comparison
Same inputs, every formula — see how much they agree.
Your likely TDEE range
BMR × activity, from sedentary to very active.
Your true maintenance calories sit somewhere in this range. Use our TDEE calculator for a precise number.
Estimates based on published formulas (Mifflin-St Jeor, Harris-Benedict, Katch-McArdle). Individual results vary ±10–15%. Not medical advice.
What is a BMR calculator?
BMR stands for basal metabolic rate: the number of calories your body burns at complete rest just to keep you alive. Breathing, circulating blood, regulating body temperature, repairing cells — all of it costs energy, and that cost is your BMR. A BMR calculator estimates this number from your age, sex, height and weight, so you know your metabolic floor before planning any diet. For most people BMR accounts for roughly 60 to 70 percent of total daily calorie burn, which makes it the single biggest piece of your energy expenditure.
BMR vs TDEE vs RMR — what the BMR calculator tells you
These three get mixed up constantly. BMR is measured under strict lab conditions: complete rest, fasting, thermally neutral room. RMR (resting metabolic rate) is the practical cousin — measured at rest but without the strict lab protocol, and it usually lands about 10 percent higher than BMR. TDEE (total daily energy expenditure) is BMR multiplied by your activity level, and it represents what you actually burn in a real day. Think of it as a ladder: BMR is the floor, RMR sits slightly above it, and TDEE is the number you plan your diet around. Once you have your BMR from the calculator above, use our TDEE calculator to add activity and get your full daily burn.
Which BMR formula should you use in the calculator?
Mifflin-St Jeor
Developed in 1990 and validated against hundreds of subjects, this is the default choice of most dietitians — and the default in our BMR calculator. Use it if you want one reliable number without extra measurements.
Revised Harris-Benedict
The 1984 revision of the 1919 original. A classic that tends to estimate slightly higher than Mifflin-St Jeor. Still widely cited in clinical settings, and available as an option in the BMR calculator above.
Katch-McArdle
The most accurate option — but only if you know your body fat percentage, because it calculates from lean body mass instead of total weight. If you lift weights or are very lean, this formula deserves your attention. Tick the body fat box in the BMR calculator to unlock it.
What affects the number your BMR calculator gives you?
Muscle tissue burns more calories at rest than fat tissue, so muscular people have higher BMRs at the same weight. Men typically have higher BMRs than women of the same size, largely because of greater average muscle mass. BMR declines with age — roughly 1 to 2 percent per decade after early adulthood — as muscle mass naturally decreases. Very low calorie diets can also suppress BMR temporarily, which is one reason crash diets backfire. This is why the BMR calculator asks for age and sex: both shift the result meaningfully.
How to use your BMR calculator result
Your BMR is a starting point, not a calorie target. Multiply it by an activity factor (1.2 for sedentary up to 1.9 for very active) to estimate your TDEE, then set your goal from there: eat near TDEE to maintain, moderately below it to lose fat, or slightly above it to gain muscle. Never plan to eat below your BMR for extended periods without professional guidance. Ready for the next step? Split your target calories into protein, carbs and fat with our macro calculator.
BMR calculator — frequently asked questions
What is BMR?
BMR (basal metabolic rate) is the number of calories your body burns at complete rest to keep you alive — breathing, circulation, temperature regulation and cell repair. It is typically 60 to 70 percent of your total daily calorie burn. A BMR calculator estimates it from your age, sex, height and weight.
What is the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE (total daily energy expenditure) is BMR multiplied by your activity level, and it reflects your real-world daily burn. BMR is the floor; TDEE is the number you plan meals around.
Which BMR formula is most accurate?
Mifflin-St Jeor is the best validated for the general population. Katch-McArdle is the most accurate if you know your body fat percentage, especially for lean or muscular people, because it calculates from lean body mass. Our BMR calculator offers all three so you can compare.
Should I eat below my BMR to lose weight faster?
No. Consistently eating below BMR risks muscle loss, fatigue, hormonal disruption and a slowed metabolism. A moderate deficit of 300 to 500 calories below your TDEE is safer and more sustainable.