BMI & BMR Calculator
Calculate your BMI (Body Mass Index), BMR (Basal Metabolic Rate), and daily calorie needs (TDEE) in one tool. Uses the modern Mifflin-St Jeor BMR formula and applies Asian-Indian BMI thresholds — which are stricter than WHO global numbers because South Asians develop metabolic risks at lower BMI levels.
How this calculator works
Three different metrics, three different uses:
BMI (Body Mass Index)
Formula: weight (kg) ÷ height² (m²)
BMI is a quick body-weight category indicator. Asian-Indian thresholds (per ICMR guidelines):
| BMI Range | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 22.9 | Normal weight |
| 23 – 24.9 | Overweight (Asian) |
| 25 – 29.9 | Obese Class I |
| ≥ 30 | Obese Class II/III |
The WHO global threshold is 25 for overweight and 30 for obese. ICMR's Indian thresholds are stricter — 23 and 25 — because Indians develop diabetes and cardiac issues at lower BMI than Caucasians.
BMR (Basal Metabolic Rate)
Calories your body burns at complete rest just to stay alive. Mifflin-St Jeor formula (most accurate for adults):
Men: BMR = (10 × weight) + (6.25 × height_cm) − (5 × age) + 5
Women: BMR = (10 × weight) + (6.25 × height_cm) − (5 × age) − 161
TDEE (Total Daily Energy Expenditure)
Your maintenance calorie need — BMR multiplied by an activity factor:
- Sedentary (desk job): BMR × 1.2
- Light (1-3 days/week light exercise): BMR × 1.375
- Moderate (3-5 days/week): BMR × 1.55
- Very active (6-7 days/week intense): BMR × 1.725
- Extra active (physical job + training): BMR × 1.9
For weight loss, eat 500 kcal below TDEE (≈ 0.5 kg loss/week). For weight gain, eat 500 kcal above TDEE.
Worked example
Example — 30-year-old man, 170 cm, 75 kg, light activity:
- BMI = 75 / (1.70 × 1.70) = 25.9 — Obese Class I (Asian)
- BMR = (10×75) + (6.25×170) − (5×30) + 5 = 750 + 1062.5 − 150 + 5 = 1668 kcal/day
- TDEE = 1668 × 1.375 = 2293 kcal/day
- For weight loss: 1793 kcal/day target
- Healthy weight range (BMI 18.5-22.9): 53.5 – 66.2 kg
Frequently asked questions
Why are Indian BMI thresholds stricter than WHO?
South Asians (including Indians) tend to have higher body fat percentage and visceral fat at lower BMI than Caucasians. ICMR guidelines (2009 onwards) recommend 23 as overweight and 25 as obese threshold for Indians, instead of WHO's 25/30. This better predicts diabetes and cardiac risk in Indian populations.
Is BMI accurate for muscular people?
No. BMI doesn't differentiate between fat and muscle. Athletes and bodybuilders often have BMI in the obese range despite very low body fat. For them, body fat percentage (via DEXA scan, calipers, or smart scales) is a much better measure.
Should pregnant women use this calculator?
No. BMI and BMR formulas are not meant for pregnant or breastfeeding women. Calorie needs vary significantly during pregnancy — consult an obstetrician or registered dietitian for guidance.
Why does BMR drop with age?
Lean muscle mass declines as you age (sarcopenia), and muscle is the most metabolically active tissue. From age 30 onwards, BMR drops about 1-2% per decade. This is why older adults often gain weight on the same calorie intake they had at 25.
What if I want to lose weight faster than 0.5 kg/week?
More aggressive deficits (750-1000 kcal/day below TDEE) work but come with risks: muscle loss, low energy, hormonal disruption, especially in women. A 500 kcal deficit is the safest sustainable rate. Combine with strength training to preserve muscle mass.
How do I increase my TDEE?
Three levers: (1) Increase muscle mass via strength training — adds 50-100 kcal/day per kg of muscle gained. (2) Add NEAT (non-exercise activity thermogenesis) — walk more, take stairs, stand often. (3) Add structured exercise. Cardio burns calories during exercise; strength training burns long-term via raised BMR.
Should I trust my smartwatch's calorie burn?
Smartwatches systematically over-estimate calories burned, often by 30-50% for non-running activities. Use them for trends, not absolute numbers. The TDEE formula here is more reliable as a starting baseline.
What is a healthy BMI for Indian women specifically?
Same range — 18.5 to 22.9. The ICMR thresholds don't differ by gender. However, women naturally have higher essential body fat percentage than men (12-15% vs 5-8%), so a woman at BMI 22 may have 25-30% body fat, which is normal and healthy.