Pregnancy Weight Gain Calculator
Recommended weight-gain range during pregnancy by pre-pregnancy BMI category — Institute of Medicine 2009 guidelines.
Result
- Pre-pregnancy BMI23.30
- BMI categoryNormal (BMI 18.5-24.9)
- Current gestational week20 (Second trimester)
- Total recommended gain25.0 lb – 35.0 lb
- — Expected gain to this week —
- First-trimester contribution3.0 lb (typical)
- Weekly rate after week 131.0 lb/wk
- Expected gain at week 208.5 lb – 11.5 lb (midpoint 10.0 lb)
- SourceIOM 2009 — Rasmussen & Yaktine (eds.), "Weight Gain During Pregnancy: Reexamining the Guidelines"
Step-by-step
- BMI = weight_kg / height_m² = 63.50 / 1.6510² = 23.30.
- Match BMI to IOM 2009 category → Normal (BMI 18.5-24.9).
- Total range: 25.0 lb – 35.0 lb over the full pregnancy.
- Expected to week 20: first trimester (~3.0 lb) + 7 wk × 1.0 lb/wk = midpoint 10.0 lb.
How to use this calculator
- Enter your pre-pregnancy weight (best from a doctor visit shortly before conception, or first prenatal appointment).
- Enter your height — fixed since adulthood.
- Pick your current gestational week from your last menstrual period (LMP) or ultrasound dating.
- Switch to twin if applicable — the recommended ranges shift up substantially.
- Compare actual gain to the "expected at week N" line; consult your OB if you're notably above or below.
About this calculator
The Institute of Medicine (now National Academy of Medicine) issued updated pregnancy weight-gain guidelines in 2009, replacing the older 1990 ranges. The new ranges are stratified by pre-pregnancy BMI: underweight women should gain MORE (28-40 lb total) than obese women (11-20 lb), with normal-weight at 25-35 lb. The clinical reason: total maternal-fetal weight gain affects birthweight, gestational diabetes risk, and post-partum weight retention. The first trimester typically contributes just 1-4.5 lb of total gain; the second and third trimesters add ~1 lb/wk (less for higher BMI categories). Twin pregnancies have separate, larger ranges (37-54 lb for normal pre-pregnancy BMI). These guidelines are an evidence-based target, not a strict rule — actual gain depends on appetite, nausea, fluid retention, and complications. Discuss specifics with your OB or midwife.