Pregnancy Weight Gain Calculator
Calculate recommended weight gain during pregnancy based on IOM guidelines.
Enter pre-pregnancy BMI, current weight, and gestational age to track your progress.
The Institute of Medicine (IOM) published its pregnancy weight gain guidelines in 2009, and they remain the standard used by OB/GYNs and midwives worldwide. The recommended range depends entirely on pre-pregnancy BMI — not a one-size figure.
BMI = Weight (kg) / Height (m)²
IOM recommended ranges:
- Underweight (BMI under 18.5): 28-40 lbs (12.7-18.1 kg)
- Normal weight (BMI 18.5-24.9): 25-35 lbs (11.3-15.9 kg)
- Overweight (BMI 25.0-29.9): 15-25 lbs (6.8-11.3 kg)
- Obese (BMI 30.0 or higher): 11-20 lbs (5.0-9.1 kg)
For twin pregnancies, the IOM recommends approximately 37-54 lbs for normal weight, 31-50 lbs for overweight, and 25-42 lbs for obese — roughly 50% more than singleton targets.
The pattern of gain also matters. The first trimester typically involves only 1-4 lbs of total gain. After that, the common weekly rate is roughly 1 lb per week for normal-weight women, 0.5-0.7 lbs for overweight women.
Weight gained during pregnancy comes from many sources: the baby (approximately 7-8 lbs at term), placenta (1-2 lbs), amniotic fluid (2 lbs), uterine growth (2 lbs), breast tissue (1-3 lbs), blood volume increase (3-4 lbs), and maternal fat stores (6-8 lbs for normal weight).
Gaining too little increases risk of low birth weight and preterm delivery. Gaining too much increases risk of gestational diabetes, C-section, and difficulty losing weight postpartum. This calculator is for educational purposes only — your healthcare provider will give personalized guidance based on your complete medical history.