Medically reviewed by Samantha L. Fox, RN, BSN, MSN
Nursing Informaticist · United States Navy Nurse Corps · Last reviewed
Pregnancy Weight Gain Calculator
Get personalized weight gain recommendations based on IOM guidelines and your pre-pregnancy BMI.
How the Pregnancy Weight Gain Calculator Works
Our pregnancy weight gain calculator is based on the Institute of Medicine (IOM) guidelines, which are the gold standard for weight gain recommendations during pregnancy. These guidelines, updated in 2009 and endorsed by the American College of Obstetricians and Gynecologists (ACOG), provide BMI-specific ranges that balance optimal outcomes for both mother and baby.
The calculator first determines your Body Mass Index (BMI) using the standard formula: BMI = (weight in pounds × 703) ÷ (height in inches)². Your BMI is then categorized as underweight (under 18.5), normal weight (18.5–24.9), overweight (25–29.9), or obese (30 and above). Each category has a different recommended total weight gain range and weekly gain target.
Weight gain during pregnancy is not evenly distributed across all 40 weeks. In the first trimester, most women gain only 1–5 pounds total, and some may even lose weight due to morning sickness. The majority of weight gain occurs during the second and third trimesters, when the baby is growing rapidly and your body is storing necessary resources for delivery and breastfeeding.
The recommended weekly gain rates for the second and third trimesters range from about 0.4 pounds per week for obese women to 1.3 pounds per week for underweight women. These rates reflect the different needs based on starting BMI — women who begin pregnancy underweight need to gain more to ensure adequate nutrition for the growing baby, while women who start at a higher BMI can gain less while still supporting a healthy pregnancy.
When you provide your current pregnancy week, the calculator estimates how much weight you should have gained so far. This is calculated proportionally for the first trimester and using the weekly rate for the second and third trimesters. This gives you a personalized benchmark to discuss with your healthcare provider. Remember, these are guidelines — individual variation is normal, and your doctor may adjust recommendations based on your specific health situation.
Things that help with healthy pregnancy weight
Track trend lines week-to-week without obsessing over single days.
Logging food and movement helps far more than scale-watching.
What to Eat When You're Expecting and similar evidence-based guides.
Folic acid, iron, DHA — the standard prenatal stack.
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📚Clinical Sources & References
The calculations and guidance on this page are based on current clinical standards and peer-reviewed research. Reviewed by Samantha L. Fox, RN, BSN, MSN — Emergency Department nurse and US Navy Nurse Corps officer.
- [1]Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press. 2009.
- [2]ACOG Committee Opinion No. 548: Weight Gain During Pregnancy. Obstet Gynecol. 2013;121(1):210-212.
- [3]Rasmussen KM, Yaktine AL, editors. Institute of Medicine (US) and National Research Council (US) Committee. Revised Weight Gain Targets. 2009.
- [4]Siega-Riz AM, Viswanathan M, Moos MK, et al. A systematic review of outcomes of maternal weight gain according to the Institute of Medicine recommendations. Am J Obstet Gynecol. 2009;201(4):339.e1-14.