Health & Fitness
Pregnancy Weight Gain Calculator (IOM Guidelines)
Calculate recommended pregnancy weight gain based on pre-pregnancy BMI using IOM (Institute of Medicine) 2009 guidelines. Track whether you are on track each trimester.
For informational purposes only. Always consult your healthcare provider.
Pre-pregnancy BMI: 1.7 → Underweight
IOM guidelines by BMI category
| Category | BMI | Total gain | Weekly |
|---|---|---|---|
| Underweight | < 18.5 | 28–40 lb | 0.97–1.28 lb |
| Normal weight | 18.5–24.9 | 25–35 lb | 0.77–1.10 lb |
| Overweight | 25.0–29.9 | 15–25 lb | 0.51–0.73 lb |
| Obese | ≥ 30.0 | 11–20 lb | 0.37–0.60 lb |
IOM/NAM weight gain guidelines
| Pre-pregnancy BMI | Category | Total recommended gain | Weekly rate (2nd & 3rd trimester) |
|---|---|---|---|
| < 18.5 | Underweight | 28–40 lbs (12.5–18 kg) | 1–1.3 lbs/week |
| 18.5–24.9 | Normal weight | 25–35 lbs (11.5–16 kg) | 0.8–1 lb/week |
| 25.0–29.9 | Overweight | 15–25 lbs (7–11.5 kg) | 0.5–0.7 lbs/week |
| ≥ 30.0 | Obese | 11–20 lbs (5–9 kg) | 0.4–0.6 lbs/week |
Where the weight goes
For a normal-BMI pregnancy with a 25–35 lb total gain, the weight is approximately distributed as:
- Baby: ~7.5 lbs
- Placenta: ~1.5 lbs
- Amniotic fluid: ~2 lbs
- Uterus growth: ~2 lbs
- Increased blood volume: ~4 lbs
- Breast tissue: ~2 lbs
- Fluid, fat, and protein stores: ~7 lbs
First trimester note
Minimal weight gain (0–5 lbs total) is expected and normal during the first trimester. The major portion of recommended weight gain occurs in the second and third trimesters as the baby grows rapidly. Morning sickness may temporarily reduce appetite and cause slight weight loss in the first weeks.
Twin and multiple pregnancy
Weight gain recommendations differ significantly for multiple pregnancies. For twins with a normal pre-pregnancy BMI, the IOM recommends 37–54 lbs (17–25 kg) total gain. Higher multiples require individualized guidance from a healthcare provider.