Pregnancy Weight Gain Calculator
A week-by-week schedule for healthy weight gain, based on the Institute of Medicine guidelines for your pre-pregnancy BMI. Enter your current week, height, and your weights before pregnancy and now — the calculator shows the recommended range for this week, for delivery, and for every week in between.
Pregnant with twins
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Recommended weight gain during pregnancy
Weight gain in pregnancy is normal and necessary: it supplies the nutrients for the baby's development and stores reserves for breastfeeding. But the amount matters — for each pre-pregnancy BMI range, studies find a band of total gain associated with the best outcomes for mother and baby. The usual pattern is only 1–4 pounds across the first three months, then about a pound a week for the rest of the pregnancy, supported by roughly 300 extra calories a day — a sandwich and a glass of milk, not a second dinner. The Institute of Medicine guidelines:
| Prepregnancy BMI (kg/m²) | Category | Total gain range | Total gain — twins |
|---|---|---|---|
| < 18.5 | Underweight | 28–40 lbs | — |
| 18.5–24.9 | Normal Weight | 25–35 lbs | 37–54 lbs |
| 25.0–29.9 | Overweight | 15–25 lbs | 31–50 lbs |
| ≥ 30.0 | Obese | 11–20 lbs | 25–42 lbs |
These are recommendations, not rules — gain varies between women, and a healthcare provider can tailor the target to your specific situation. (The IOM publishes no twin range for underweight pregnancies; this calculator applies the normal-weight twin range in that case.)
Complications of suboptimal gain
Too little gain can compromise the baby's growth and raises the risk of preterm birth. Too much gain can complicate labor, produce a significantly larger-than-average baby, increase the chance of a cesarean section, and leave weight that is hard to lose after delivery. The recommended band is where those risks balance.
What to eat during pregnancy
No formula guarantees a healthy baby, and general healthy eating — vegetables, fruits, whole grains, lean proteins, healthy fats — does most of the work. A few nutrients deserve special attention: folate/folic acid guards against neural tube defects and premature birth (leafy greens, citrus, beans, peas, supplements); calcium builds bones and teeth and supports circulation, muscles, and nerves (dairy, spinach, salmon, kale); vitamin D partners with calcium for bone strength (fortified milk, juice, fish, eggs); protein drives the baby's growth (lean meat, poultry, fish, eggs, beans, nuts, soy); and iron — needed at roughly double the usual intake — builds the extra blood that carries oxygen to the baby (lean red meat, poultry, fish, fortified foods, beans; vitamin C alongside plant iron improves absorption). Many people cover the gaps with a prenatal vitamin — a healthcare professional can say whether you should.
Just as important is what to avoid: high-mercury fish (the FDA names shark, swordfish, king mackerel, and tilefish; shrimp, salmon, pollock, catfish, cod, tilapia, and light canned tuna are generally considered safer); raw or undercooked seafood, meat, poultry, and eggs; unpasteurized dairy; unwashed produce and raw sprouts; and excess caffeine. Herbal teas are little studied in pregnancy. Alcohol has no proven safe level in pregnancy — it raises the risk of miscarriage, stillbirth, and fetal alcohol syndrome — and smoking before, during, or after pregnancy harms both mother and baby, from premature birth to sudden infant death syndrome. When in doubt about a food, ask a medical professional.
References
- Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press, 2009.
- Mayo Clinic. "Pregnancy weight gain: What's healthy?" mayoclinic.org.