How to use
- Choose your sex and units, then enter your age, height and weight.
- If you know your body fat percentage (from a smart scale, DEXA or calipers), enter it to add the lean-mass-based Katch-McArdle equation.
- The Mifflin-St Jeor result is shown large, with every equation compared in the table below.
This calculator provides general information only and is not medical advice.
The equations
Basal metabolic rate (BMR) is the energy your body uses at complete rest just to stay alive. W = weight in kg, H = height in cm, A = age in years.
| Equation | Men | Women |
|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A + 5 | 10W + 6.25H − 5A − 161 |
| Harris-Benedict, revised (Roza & Shizgal, 1984) | 88.362 + 13.397W + 4.799H − 5.677A | 447.593 + 9.247W + 3.098H − 4.330A |
| Katch-McArdle | 370 + 21.6 × lean mass (kg) | same |
- Mifflin-St Jeor came out as the most reliable equation in the American Dietetic Association’s evidence analysis (Frankenfield et al., 2005), predicting resting metabolic rate within 10% of measured values for more people — both non-obese and obese — than the alternatives. That is why it is the headline number.
- Harris-Benedict dates from 1918–1919. This calculator uses the 1984 revision by Roza and Shizgal, which refitted the coefficients.
- Katch-McArdle ignores sex and age and uses lean body mass (weight × (1 − body fat %)), so it diverges most for very muscular or very lean people.
Example
Woman, 30, 163 cm (5 ft 4 in), 57 kg (126 lb), 28% body fat:
| Equation | Working | Result |
|---|---|---|
| Mifflin-St Jeor | 570 + 1,018.75 − 150 − 161 | 1,277.75 kcal |
| Harris-Benedict, revised | 447.593 + 527.079 + 504.974 − 129.9 | ≈ 1,350 kcal |
| Katch-McArdle | 370 + 21.6 × 41.04 | ≈ 1,256 kcal |
A 40-year-old man at 175 cm (5 ft 9 in) and 75 kg (165 lb) gets 1,648.75 kcal from Mifflin-St Jeor and about 1,706 kcal from revised Harris-Benedict.
Things to keep in mind
- Every equation is an estimate based on population averages. Only indirect calorimetry (measuring the oxygen you use) gives your actual figure.
- Harris-Benedict usually comes out a little higher than Mifflin-St Jeor. Treat the spread as a range rather than picking a “right” number.
- The equations were built for adults. They may not fit teenagers, pregnancy or conditions that affect metabolism, such as thyroid disease — ask a health professional in those cases.
FAQ
Should I eat only my BMR to lose weight?
No. BMR is only part of what you burn; daily activity and digestion add a lot on top. For total daily needs and goal targets, use the calorie calculator.
Why does my smart scale show a different BMR?
Body composition scales plug their own lean-mass estimate into a proprietary formula. Enter your body fat percentage to compare with Katch-McArdle, or estimate it with the body fat calculator.
Does BMR drop with age?
Yes. All three equations lower BMR as age rises, and losing muscle with age lowers it further.