Enter your details and this calculator returns your basal metabolic rate from all three major formulas simultaneously, then multiplies the Mifflin–St Jeor figure across five standard activity levels to give practical daily calorie targets. Results update as you type — no submit button, no signup. Pair it with our calorie calculator to plan a deficit or surplus, or our macro calculator to split those calories into protein, carbs and fat.
BMR Calculator
Your basal metabolic rate from three peer-reviewed formulas, plus daily calorie targets for every activity level.
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Your BMR
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Harris–Benedict—
Katch–McArdle—
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Daily calories by activity level
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What BMR actually measures
Basal metabolic rate is the energy your body burns at complete rest — breathing, circulation, cell repair, temperature regulation. It typically accounts for 60–70% of everything you burn in a day. The rest comes from digestion (~10%) and physical activity (everything else), which is why the activity-multiplied figures above are what matter for setting calorie targets.
Why three formulas?
Mifflin–St Jeor (1990) is the headline number — validation studies, including the ADA's 2005 review, found it the most accurate for the general population. Harris–Benedict (revised 1984) is the older standard, still widely used clinically; it tends to run 5% higher. Katch–McArdle works from lean body mass instead of total weight, which makes it the best choice for lean, muscular people whose muscle mass the other formulas underestimate — but it needs a body-fat percentage to work.
Using the number
Never eat below your BMR for extended periods. For fat loss, subtract 300–500 kcal from your activity-adjusted total (not from BMR itself); for muscle gain, add 200–300. If your goal is a full energy-expenditure picture including exercise, our TDEE calculator goes deeper.
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Frequently asked questions
What is a normal BMR?
Most adult women fall between 1,200–1,500 kcal/day and most adult men between 1,500–1,900, but the range is wide — BMR scales with body size, muscle mass, age and sex, so compare against your own number, not an average.
Which BMR formula is most accurate?
Mifflin–St Jeor for most people — it's the formula the American Dietetic Association found most reliable. If you're lean and muscular and know your body fat %, Katch–McArdle is better because it works from lean mass.
Is it safe to eat at my BMR?
Eating at BMR is an aggressive deficit since your true daily burn is always higher. Short-term it's generally tolerable for healthy adults; long-term it risks muscle loss and metabolic adaptation. Deduct from your activity-adjusted calories instead.
Why is my BMR lower as I age?
BMR declines roughly 1–2% per decade after your twenties, driven mostly by gradual muscle loss. Resistance training measurably slows the decline.
What's the difference between BMR and TDEE?
BMR is your at-rest burn. TDEE (total daily energy expenditure) is BMR plus digestion and all activity — it's the number you actually eat against. The activity-level table above is your estimated TDEE at each level.