Best Free BMI Calculator Online
BMI is a quick population-level screening metric — not a full health assessment. The best calculators give you the number, explain the category, and note the limitations.
Calculators compared
| Tool | Metric + Imperial | BMI category | Health context | Privacy |
|---|---|---|---|---|
| Irreva | ✅ | ✅ | ✅ Noted | Browser |
| CDC BMI Calculator | ✅ | ✅ | ✅ Detailed | No tracking |
| NHS BMI Calculator | ✅ | ✅ (UK ranges) | ✅ | UK server |
| RapidTables | ✅ | Basic | Minimal | No upload |
What BMI gets right — and wrong
- ✅ Quick population screening for underweight/obesity
- ✅ Consistent, reproducible formula
- ⌠Doesn't account for muscle mass — athletes often read as 'overweight'
- ⌠Less accurate for the elderly (muscle loss changes interpretation)
- ⌠BMI ranges were derived from mostly European populations
When to use BMI vs other metrics
Use BMI as a starting point, then complement with waist-to-height ratio or body fat percentage for a fuller picture. For children, use age- and sex-specific BMI percentiles, not adult thresholds.
Frequently Asked Questions
Is a BMI of 25 actually overweight?
By WHO classification, 25–29.9 is 'overweight.' Context matters — a muscular person at 25.5 BMI is not the same health risk as a sedentary person at the same number.
Does Irreva store health data?
No. BMI calculation runs locally; height and weight are never sent anywhere.