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BMI Calculator
Body Mass Index with WHO classification and healthy weight range.
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BMR Calculator
Basal Metabolic Rate — calories your body burns at rest. No signup — your inputs stay in your browser.
Step By Step
How to Use This Calculator
4 steps
- Select your biological sex, then enter age, height, and weight.
- Height can be entered in cm or ft + in — use the toggle to switch.
- Body fat % is optional. If you know it, enter it to unlock the Katch–McArdle result.
- Compare all three formula results — Mifflin–St Jeor is recommended for most people.
Worked Example
Example: 30-year-old male, 175 cm, 75 kg
Use this sample to sanity-check your inputs and understand what the final result represents.
- 1Sex: Male · Age: 30 · Height: 175 cm · Weight: 75 kg
- 2Mifflin–St Jeor: (10×75) + (6.25×175) − (5×30) + 5 = 1,773 kcal
- 3Harris–Benedict: 88.362 + (13.397×75) + (4.799×175) − (5.677×30) = 1,882 kcal
- 4Katch–McArdle (15% body fat): 370 + 21.6 × (75 × 0.85) = 1,748 kcal
Final Result
Mifflin result: ~1,773 kcal/day at complete rest. Multiply by activity factor for total daily needs.
Methodology
Mifflin–St Jeor, Harris–Benedict & Katch–McArdle
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
Mifflin–St Jeor (1990) — Male: (10 × kg) + (6.25 × cm) − (5 × age) + 5; Female: same − 161. Harris–Benedict revised (Roza & Shizgal, 1984) — Male: 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age). Katch–McArdle (1975) — 370 + (21.6 × lean mass kg); lean mass = weight × (1 − body fat ÷ 100). Mifflin is recommended for general use; Katch–McArdle suits athletes who know their body fat percentage.
Frequently Asked Questions
What is BMR and why does it matter?+
BMR (Basal Metabolic Rate) is the number of calories your body burns in a full day of complete rest — just to keep your heart beating, lungs breathing, and organs functioning. It's the floor of your calorie needs. Knowing it helps you set a realistic calorie target, because eating below your BMR for extended periods can slow metabolism and cause muscle loss.
Which formula is most accurate — Mifflin, Harris-Benedict, or Katch-McArdle?+
For most people, Mifflin–St Jeor (1990) is the most accurate. A 2005 review in the Journal of the American Dietetic Association (Frankenfield et al.) found it predicted resting energy expenditure within 10% for 82% of subjects — better than the original Harris–Benedict. Katch–McArdle can be more accurate if you know your body fat percentage, because it uses lean mass instead of total weight, making it better for athletes or people with high muscle mass.
What is the difference between BMR and TDEE?+
BMR is calories burned at complete rest. TDEE (Total Daily Energy Expenditure) is your actual daily burn including movement, exercise, and digestion. TDEE = BMR × an activity multiplier — typically 1.2 for sedentary up to 1.9 for very active. Eating at TDEE maintains your weight; eating below it creates a deficit for fat loss.
Why do I need to enter body fat percentage?+
Body fat % is optional and only used for the Katch–McArdle formula, which calculates BMR from lean mass rather than total body weight. If you skip it, you still get Mifflin and Harris–Benedict results. If you know your body fat (from a DEXA scan, calipers, or a smart scale), entering it gives you a third data point that tends to be more accurate for muscular or athletic builds.
Does BMR change with age?+
Yes, gradually. BMR typically decreases with age, mainly because muscle mass tends to decline from the mid-30s onward (a process called sarcopenia). Less muscle means lower resting energy needs. Strength training is one of the most effective ways to slow this decline.
Can I use this result to plan a diet?+
Use it as a starting estimate, not a prescription. Individual metabolism varies based on genetics, hormones, gut microbiome, and medical conditions — none of which these formulas can capture. A common approach is to track weight for 2–3 weeks at a given calorie level and adjust from there. A registered dietitian can give personalised guidance.