Online Tool Store
BMR Calculator
Calculate your Basal Metabolic Rate using the Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas side by side. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Example shown — replace it with your own numbers.
How it works
- Enter your sex, age, height, and weight.
- Optionally enter your body fat percentage to also see the Katch-McArdle estimate.
- All three formulas update together as you type, so you can compare them side by side.
The formulas
Mifflin-St Jeor (1990):
Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
Harris-Benedict, revised 1984:
Men: BMR = 88.362 + 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age
Women: BMR = 447.593 + 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age
Katch-McArdle (needs body fat %):
Lean body mass = weight × (1 − body fat % / 100)
BMR = 370 + 21.6 × lean body mass (kg)
Example: a 32-year-old man, 170 cm and 82 kg, with 22% body fat, gets roughly 1,728 kcal/day from Mifflin-St Jeor, 1,821 kcal/day from Harris-Benedict, and 1,752 kcal/day from Katch-McArdle — a reminder that these are estimates from different models, not one single "correct" number.
FAQ
What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body burns at complete rest — just staying alive. TDEE (Total Daily Energy Expenditure) adds your activity level on top of BMR to estimate your full daily calorie burn. This tool calculates BMR only; for a daily calorie target that includes activity level and a weight-loss goal, see the Calorie Deficit Calculator.
Which formula should I trust?
Mifflin-St Jeor is the one most current nutrition guidelines recommend as the most accurate for the general population, and it's a reasonable default. Harris-Benedict is older and tends to run slightly higher. Katch-McArdle can be more accurate if you know your body fat percentage, since it accounts for body composition directly rather than estimating it from age and sex.
Why does Katch-McArdle show a dash until I enter something?
Katch-McArdle is calculated from lean body mass, which needs your body fat percentage to work out — without it, there's nothing to calculate. Mifflin-St Jeor and Harris-Benedict don't need body fat % and always show a result.
Where would I get my body fat percentage from?
A body composition scale, a skinfold caliper measurement, or a DEXA scan are common sources — accuracy varies quite a bit between methods. If you only have a rough estimate, treat the Katch-McArdle result as approximate too.
Is my information sent anywhere?
No. All three formulas are calculated locally in your browser with plain JavaScript — none of your age, weight, height, or body fat percentage is uploaded or logged.
How we compare
| Feature | Online Tool Store | Typical fitness app calculators | Single-formula BMR calculators |
|---|---|---|---|
| No sign-up or app install | ✓ | ✗ | ✓ |
| Shows three formulas side by side | ✓ | ✗ (usually one) | ✗ (one formula) |
| Free, no premium tier, no ads | ✓ | Varies — many gate detailed breakdowns | ✓ |
Most calculators pick one formula for you. Seeing all three side by side — and how much they actually disagree — gives a more honest picture than a single confident-looking number.