Pregnancy Weight Gain Calculator

The Institute of Medicine (IOM) 2009 guidelines recommend different total gains based on pre-pregnancy BMI: underweight (BMI < 18.5): 28–40 lbs; normal weight (18.5–24.9): 25–35 lbs; overweight (25–29.9): 15–25 lbs; obese (≥ 30): 11–20 lbs. These ranges account for the fact that women with more body fat stores need to gain less to supply the growing baby.

Most women gain only 1–5 lbs in the first trimester (weeks 1–13). The baby is tiny during this period — 1st trimester weight changes are mainly due to increased blood volume, uterine growth, and breast tissue. Nausea can reduce appetite and some women gain nothing (or even lose weight) in the first trimester, which is generally fine.

A typical gain of 25–35 lbs breaks down roughly as: baby 7–8 lbs, placenta 1.5 lbs, amniotic fluid 2 lbs, uterus growth 2 lbs, breasts 2 lbs, blood volume increase 4 lbs, fluid retention 4 lbs, maternal fat stores 7 lbs. Only the fat stores and some fluid remain postpartum.

Excessive gestational weight gain increases the risk of gestational diabetes, preeclampsia, emergency C-section, large-for-gestational-age babies, postpartum weight retention, and childhood obesity in the baby. It doesn't mean these outcomes will happen, but the risks are meaningfully higher.

Insufficient weight gain is associated with preterm birth, small-for-gestational-age babies, and low birthweight. Underweight women who don't gain enough weight have the highest risk. Regular prenatal care and working with your OB or midwife is the best way to monitor this.

No — the IOM 2009 guidelines cover singleton pregnancies only. Twin pregnancy weight gain recommendations are higher: normal BMI 37–54 lbs, overweight 31–50 lbs, obese 25–42 lbs. For twins or multiples, always follow your obstetric provider's guidance, which may differ from general charts.