Free BMI Calculator
Check your Body Mass Index instantly — based on CDC & WHO guidelines
Ready to Calculate
Enter your height and weight to see your BMI result.
What Is BMI?
Body Mass Index (BMI) is a screening tool recommended by the CDC and WHO to estimate body fat based on your weight-to-height ratio. It's calculated by dividing your weight in kilograms by the square of your height in meters. While not a diagnostic tool, BMI correctly identifies weight-related health risks in approximately 75–80% of the adult population.
BMI Limitations
BMI does not differentiate between muscle and fat. Athletes with high muscle mass may show an "overweight" BMI despite having low body fat. It also doesn't account for age (older adults may need different thresholds), ethnicity (Asian populations face risks at lower BMIs), or fat distribution. For a complete assessment, combine BMI with waist circumference and consult a healthcare provider.
How to Calculate BMI Manually
Metric Formula
Imperial Formula
Example: A person weighing 70 kg and 1.75 m tall.
70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86 BMI (Healthy Weight)
BMI Categories & Health Risk Levels
These BMI categories are defined by the CDC and WHO for adults aged 20 and older. Your BMI number places you in one of these ranges — but remember, BMI is a screening tool, not a diagnosis.
| Category | BMI Range (kg/m²) | Health Risk Level |
|---|---|---|
| Underweight | Less than 18.5 | Nutritional deficiency, osteoporosis risk |
| Healthy Weight | 18.5 – 24.9 | Lowest risk — maintain current habits |
| Overweight | 25.0 – 29.9 | Moderately increased risk for metabolic conditions |
| Obese Class I | 30.0 – 34.9 | Significantly increased risk |
| Obese Class II | 35.0 – 39.9 | Severely increased risk |
| Obese Class III | 40.0 or higher | Very high risk — medical guidance essential |
Note for Asian populations: The WHO recommends adjusted thresholds — overweight risk begins at BMI 23, not 25. Learn more about ethnicity-based BMI thresholds →
Health Risks of Overweight & Obesity
- Type 2 Diabetes and Insulin Resistance (2–6× higher risk)
- High Blood Pressure / Hypertension (2–6× higher risk)
- Cardiovascular Disease and Stroke (2–3× higher risk)
- Sleep Apnea and Breathing Problems (3–5× higher risk)
- Joint Pain, Osteoarthritis, and Certain Cancers
Health Risks of Being Underweight
- Malnutrition and Vitamin Deficiencies
- Weakened Immune System
- Osteoporosis (Weak Bones)
- Fertility and Reproductive Health Issues
- Delayed Wound Healing and Recovery
What to Do After Getting Your BMI
Your BMI number is a starting point — here's what action to take based on your result:
| Your BMI | Recommended Action | Helpful Tool |
|---|---|---|
| < 18.5 | Track calorie intake; consult doctor if unintentional | Calorie Calculator → |
| 18.5 – 24.9 | Maintain current habits; check annually | Ideal Weight Calculator → |
| 25.0 – 29.9 | Calculate TDEE; set modest calorie deficit | TDEE Calculator → |
| 30.0 – 34.9 | Set 6-month goal; track macros; consult GP | Macro Calculator → |
| 35.0+ | Medical consultation recommended first | Consult healthcare provider |
For a deeper understanding of your BMI number, read our complete BMI Health Guide — covering BMI exceptions, Asian-adjusted thresholds, and step-by-step action plans.
Frequently Asked Questions
Sources & Data
BMI categories and health risk data in this calculator are based on:
- CDC — About Adult BMI — classification standards and prevalence data
- WHO — Body Mass Index Classification — international BMI thresholds
- NHLBI / NIH — BMI Tables — US standard formula and health risk associations