Pregnancy Weight Gain by Week (IOM Guidelines)
Recommended cumulative pregnancy weight gain by gestational week and pre-pregnancy BMI, per the 2009 Institute of Medicine (IOM/NAM) singleton and twin pregnancy guidelines.
Current 0 lb: Below recommended range
Per Institute of Medicine (now NAM) 2009 Weight Gain During Pregnancy: Reexamining the Guidelines, endorsed by ACOG Committee Opinion 548 (reaffirmed 2023). Singleton ranges from Table S-1; twin from IOM provisional Table S-2; weekly rates from IOM Table 1. Not a substitute for prenatal medical care.
General calculation reads
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About this tool
The 2009 Institute of Medicine (now National Academy of Medicine) guidelines on Weight Gain During Pregnancy stratify recommended gestational weight gain by pre-pregnancy BMI category: underweight (BMI < 18.5) → 28–40 lb total (12.5–18 kg); normal weight (18.5–24.9) → 25–35 lb (11.5–16 kg); overweight (25.0–29.9) → 15–25 lb (7–11.5 kg); and obese (≥30.0) → 11–20 lb (5–9 kg). For twin pregnancies the bands shift up: normal BMI 37–54 lb, overweight 31–50 lb, obese 25–42 lb. The recommended rate after the first trimester is roughly linear: 1 lb/week for underweight + normal, 0.6 lb/week for overweight, 0.5 lb/week for obese. First-trimester (weeks 0–13) gain is typically 1.1–4.4 lb regardless of BMI. ACOG (Committee Opinion 548, reaffirmed 2023) endorses these IOM ranges as standard prenatal practice. Weight outside these bands is associated with gestational diabetes, preeclampsia (above range) or small-for-gestational-age birth (below range), but individual variation is wide — discuss specific targets with your obstetric provider.
How to use it
- Enter pre-pregnancy weight in pounds and height (or pre-pregnancy BMI if known).
- Enter current gestational week (1–40).
- Read your IOM-recommended cumulative gain range and weekly target.
- Discuss with your OB/midwife — these are population-level guidelines, not individual prescriptions.
Frequently asked questions
- What if my pre-pregnancy BMI was unknown?
- Estimate from your typical adult weight before pregnancy. Most OB practices use the weight at the first prenatal visit if it falls in the first 4 weeks.
- Do these apply to twins?
- Toggle the twin pregnancy option. The IOM published provisional twin ranges in 2009; ACOG continues to use them.
- I am gaining outside the range — is that bad?
- Outside the range is associated with higher risk of gestational diabetes, preeclampsia, macrosomia (above) or low birth weight (below), but the absolute risk increase is modest. Trends matter more than single readings.
- What about week-by-week distribution?
- First trimester: 1–4 lb total. Second trimester: ~0.5–1 lb/week. Third trimester: same as second. The rate-per-week numbers here apply to weeks 14–40.
- Is data sent anywhere?
- No. All math runs in your browser.