Pregnancy Weight Gain Calculator
About the Pregnancy Weight Gain Calculator
This calculator follows the Institute of Medicine (IOM) guidelines for gestational weight gain based on your pre-pregnancy BMI category. Appropriate weight gain supports healthy fetal development and reduces complications.
The Formula
BMI = (weight in lbs / (height in inches)²) × 703. IOM guidelines recommend: Underweight (BMI < 18.5): 28–40 lbs total; Normal (18.5–24.9): 25–35 lbs; Overweight (25–29.9): 15–25 lbs; Obese (≥ 30): 11–20 lbs. First trimester gain is about 1–4.5 lbs, followed by steady weekly gain.
Frequently Asked Questions
What if I gain too little or too much weight?
Inadequate gain may increase risk of low birth weight, while excessive gain raises the risk of gestational diabetes, preeclampsia, and Cesarean delivery. Consult your healthcare provider for personalized recommendations.
Do the guidelines differ for multiples?
Yes. For twins, IOM recommends: Normal BMI: 37–54 lbs; Overweight: 31–50 lbs; Obese: 25–42 lbs. Underweight twin guidelines are not well-established; consult your provider.