BMR Calculator
Your basal metabolic rate — the calories you burn doing nothing at all — across three validated formulas.
About you
Add it to switch to the lean-mass Katch-McArdle formula.
Activity
Goal & nutrition
Your BMR
Calories burned at complete rest
BMR (at rest)
Mifflin-St Jeor
TDEE (maintenance)
Burned per day
Adjustment
vs maintenance
Weekly change
stable
Maintenance at each activity level
Most people sit between two of these. If the scale isn't moving, you're likely closer to the lower number.
How it works
BMR is estimated from your sex, weight, height, and age. The default Mifflin-St Jeor equation is the most accurate predictor for the general population. If you enter a body-fat percentage, the calculator switches to Katch-McArdle, which ignores fat tissue (metabolically near-inert) and predicts from lean body mass instead — more accurate for athletes and very lean or very heavy people.
Mifflin-St Jeor (BMR)
BMR = 10·kg + 6.25·cm − 5·age + s
- kg / cm
- weight in kilograms, height in centimetres
- age
- age in years
- s
- +5 for men, −161 for women
Worked example
- Man, 30, 80 kg, 180 cm
- BMR = 10·80 + 6.25·180 − 5·30 + 5
- = 800 + 1,125 − 150 + 5
BMR ≈ 1,780 calories/day at complete rest.
Good to know
- BMR is a prediction, not a measurement — a metabolic cart (indirect calorimetry) is the only way to know yours exactly. Expect roughly ±10% variance.
- Katch-McArdle needs an accurate body-fat figure; a bad estimate makes it less accurate than Mifflin, not more.
- To turn BMR into a daily calorie target, multiply by your activity factor — switch to the TDEE or Calorie tabs above.
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Frequently Asked Questions
What is BMR?
Basal metabolic rate is the number of calories your body burns at complete rest just to keep you alive — breathing, circulation, cell repair, brain function. It is the largest single component of your daily calorie burn, usually 60–70% of the total.
What’s the difference between BMR and TDEE?
BMR is your burn at rest. TDEE (total daily energy expenditure) is BMR plus the calories from movement, exercise, and digestion. You eat to your TDEE, not your BMR — but BMR is the foundation the whole calculation is built on.
Which BMR formula should I use?
Mifflin-St Jeor is the most accurate for most people and is the default. Harris-Benedict is the older classic and runs slightly higher. Katch-McArdle is the best choice if you know your body-fat percentage, because it works from lean body mass — the tissue that actually drives metabolism.
Should I eat at my BMR to lose weight?
No. Eating at or below your BMR for long periods is unnecessarily aggressive and hard to sustain. Base your deficit on your TDEE instead, and keep intake above the safety floor of 1,500 calories (men) or 1,200 (women).
Why does BMR fall with age and dieting?
You lose lean muscle as you age and when you diet, and muscle is metabolically expensive. Less muscle means a lower BMR — which is why resistance training and adequate protein matter for keeping your metabolism up.