Estimate recommended total and weekly pregnancy weight gain based on your pre-pregnancy BMI using IOM 2009 guidelines.
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Based on IOM 2009 gestational weight-gain guidelines. Discuss your personal weight-gain goals with your midwife or obstetrician — these figures are population averages and individual circumstances vary widely.
Also in Fertility & Pregnancy
Health — Pregnancy
How much weight to gain during pregnancy depends on pre-pregnancy body weight. Gaining within the recommended range is associated with better outcomes for both mother and baby — including reduced risk of gestational diabetes, caesarean delivery, and complications for the newborn. This calculator uses the Institute of Medicine (IOM) 2009 guidelines, the most widely used clinical reference.
Underweight women (BMI below 18.5) are advised to gain 12.7–18.1 kg (28–40 lbs) in total. Normal weight women (18.5–24.9) should aim for 11.3–15.9 kg (25–35 lbs). Overweight women (25–29.9) are advised to gain 6.8–11.3 kg (15–25 lbs), and women with obesity (BMI ≥30) 5.0–9.1 kg (11–20 lbs). For twin pregnancies, recommended ranges are higher: 16.8–24.5 kg for normal-weight women, with different targets for other BMI categories.
Most guidance focuses on the second and third trimesters, when weekly gain becomes clinically relevant. In the first trimester, total gain of 0.5–2 kg is typical across BMI categories. In the second and third trimesters, the IOM recommends weekly gains of 0.36–0.45 kg for normal-weight women, 0.45–0.59 kg for underweight women, and 0.23–0.32 kg for overweight women.
Total weight gained is not simply body fat. By 40 weeks, weight gain includes the baby (typically 3.2–3.8 kg), placenta (around 0.7 kg), amniotic fluid (around 0.8 kg), expanded blood volume (1.8 kg), uterine growth (0.9 kg), breast tissue (0.9 kg), and fluid retention. Fat stores — needed for breastfeeding — account for around 2–4 kg for normal-weight women.
Frequently asked questions
Gaining significantly above the recommended range increases risk of gestational diabetes, hypertension, large-for-gestational-age babies (which increases caesarean rates), and difficulty losing weight postpartum. Gaining below the range is associated with preterm birth and small-for-gestational-age babies. Both extremes are worth discussing with your midwife or obstetrician.
Yes. Underweight women have higher recommended total gains and weekly gain rates than other BMI groups. Adequate nutrition and sufficient caloric intake are particularly important in this group. Regular monitoring by a healthcare provider is especially important.
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