How to use this calculator
- 1
Enter your demographics
Age, sex, height, and weight (in any unit — toggle imperial or metric).
- 2
Add body fat % (optional)
If you know your body fat percentage, enter it to unlock the Katch-McArdle formula, which is the most accurate for lean individuals.
- 3
Compare formulas
See your BMR from Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle side-by-side, with the recommended formula highlighted.
What this calculator gives you
- Three formulas calculated simultaneously
- Smart formula recommendation based on your inputs
- Optional body fat % for Katch-McArdle precision
- Calorie floor warnings (do not eat below BMR for sustained periods)
- Free, no signup, runs in your browser
Formulas used
Mifflin-St Jeor (recommended default)
Men: BMR = 10×kg + 6.25×cm − 5×age + 5 Women: BMR = 10×kg + 6.25×cm − 5×age − 161
Best for: General adult population — most accurate within ±10%
Harris-Benedict (revised)
Men: BMR = 88.362 + 13.397×kg + 4.799×cm − 5.677×age Women: BMR = 447.593 + 9.247×kg + 3.098×cm − 4.330×age
Best for: Historical reference; overestimates sedentary BMR by ~5%
Katch-McArdle
BMR = 370 + 21.6 × LBM(kg)
Best for: Lean / athletic individuals with a known body fat %
Frequently asked questions
What is BMR?+
Basal Metabolic Rate is the calories your body burns at complete rest just to keep vital organs and tissues functioning — heart, brain, lungs, kidneys, and so on. It is typically 60–75% of total daily calorie burn.
What is the difference between BMR and RMR?+
BMR is measured under strict laboratory conditions (12-hour fast, lying supine, fully relaxed). RMR (Resting Metabolic Rate) is measured under more relaxed conditions and is typically 5–10% higher than BMR. The two terms are often used interchangeably online.
Which BMR formula is most accurate?+
Mifflin-St Jeor is the most accurate for the general population (±10%). Katch-McArdle is more accurate for lean and athletic individuals because it uses lean body mass directly. Harris-Benedict tends to overestimate BMR for sedentary people.
Should I eat below my BMR?+
No, not for sustained periods. Eating below BMR for more than 2–3 weeks at a time risks micronutrient deficiencies, hormonal disruption, and accelerated muscle loss. Most adult women should not eat below 1,200 kcal; most men below 1,500 kcal.
Want the full guide?
The complete article goes deeper into the science, with charts, comparisons, and practical examples.
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