Body Mass Index (BMI) Calculator
BMI & Weight Gain Charts
BMI Category (NIH / CDC)
| BMI | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 - 24.9 | Normal |
| 25 - 29.9 | Overweight |
| 30 - 34.9 | Obesity I |
| 35 - 39.9 | Obesity II |
| >= 40 | Obesity III |
WHO Obesity Risk Classification
| BMI | Risk Category |
|---|---|
| 18.5–24.9 | Low (healthy) |
| 25.0–29.9 | Increased risk |
| 30.0–34.9 | High risk |
| 35.0–39.9 | Very high risk |
| ≥ 40 | Extremely high risk |
Institute of Medicine (IOM) Weight Gain Recommendations — Singleton Pregnancy
| Pre-pregnancy BMI | Total Gain (lbs) | Rate of Gain (2nd–3rd Trimester) |
|---|---|---|
| Underweight < 18.5 | 28–40 lbs | 1.0–1.3 lb/week |
| Normal 18.5–24.9 | 25–35 lbs | 0.8–1.0 lb/week |
| Overweight 25–29.9 | 15–25 lbs | 0.5–0.7 lb/week |
| Obesity ≥ 30 | 11–20 lbs | 0.4–0.6 lb/week |
Institute of Medicine (IOM) Weight Gain Recommendations — Twin Pregnancy
| Pre-pregnancy BMI | Total Gain (lbs) |
|---|---|
| Normal 18.5–24.9 | 37–54 lbs |
| Overweight 25–29.9 | 31–50 lbs |
| Obesity ≥ 30 | 25–42 lbs |
All calculations must be confirmed before use. These results do not substitute for clinical judgment.