Pregnancy weight gain calculator

This pregnancy weight gain calculator estimates a healthy total and week-by-week weight-gain plan based on pre-pregnancy BMI and whether you’re carrying one baby or twins. It reflects the Institute of Medicine/National Academies recommendations that are widely used by CDC and ACOG. Individual care can differ—always follow your clinician’s advice. (NCBI, National Academies Press, ACOG)

Related calculators:

How the calculator estimates your plan

The calculator classifies BMI from your pre-pregnancy height and weight, applies the IOM total-gain range for your BMI and singleton/twin status, assumes modest first-trimester gain, then spreads the remaining gain across the second and third trimesters using BMI-specific weekly rates. (NCBI, MSD Manuals)

Recommended total gain (single pregnancy)

Ranges are set by pre-pregnancy BMI:

• Underweight (BMI < 18.5): 28–40 lb (≈13–18 kg)
• Normal weight (18.5–24.9): 25–35 lb (≈11–16 kg)
• Overweight (25.0–29.9): 15–25 lb (≈7–11 kg)
• Obese (≥ 30): 11–20 lb (≈5–9 kg)

These targets come from the IOM 2009 guideline and are summarized by CDC. (CDC, NCBI)

Recommended total gain (twin pregnancy)

For twins, the guideline provides ranges for most BMI groups:

• Underweight: 37–54 lb (≈17–25 kg)
• Normal weight: 37–54 lb (≈17–25 kg)
• Overweight: 31–50 lb (≈14–23 kg)
• Obese: 25–42 lb (≈11–19 kg)

Evidence is insufficient to set a specific total-gain range for underweight twin pregnancies—your provider will individualize a plan. (CDC)

How fast to gain

• First trimester (weeks 1–12): typically little gain overall (about 0.5–2 kg total). (PMC)
• Second and third trimesters: a steady weekly pace based on BMI:
  • Underweight or normal: ~1.0 lb/week (≈0.4 kg/week)
  • Overweight: ~0.6 lb/week (≈0.27 kg/week)
  • Obese: ~0.5 lb/week (≈0.23 kg/week) (MSD Manuals, ACOG)

Where does the weight go?

Pregnancy weight isn’t just the baby. A typical breakdown includes larger breasts (1–3 lb), uterus (≈2 lb), placenta (≈1.5 lb), amniotic fluid (≈2 lb), extra blood (3–4 lb), extra body fluid (2–3 lb), and maternal fat stores (6–8 lb). Exact amounts vary by person. (Mayo Clinic)

Why staying within range matters

Both too little and too much gain are linked to higher risks—for example, small- or large-for-gestational-age births, preterm birth, cesarean delivery, and postpartum weight retention. Following a tailored target helps support healthy outcomes for parent and baby. (CDC, ACOG)

Calorie needs (general guidance)

Most people don’t need extra calories in the first trimester. On average, add about +340 kcal/day in the second trimester and +450 kcal/day in the third, focusing on nutrient-dense foods. Needs vary by body size, activity, and BMI—ask your clinician for a personalized plan. (CDC, ACOG)

Tips to stay on track

• Eat a balanced pattern (vegetables, fruits, whole grains, lean proteins, healthy fats); take a prenatal vitamin if recommended. (ACOG)
• Monitor weight regularly (same scale, similar time of day) and discuss trends with your provider. (CDC)
• Stay active as advised (e.g., walking, prenatal exercise) unless you have activity restrictions. (ACOG)
• For twins or special situations (e.g., hyperemesis, diabetes, high BMI classes), use a clinician-directed plan; weekly targets may differ. (ACOG)

Sources & further reading:
CDC: Weight Gain During Pregnancy (summary of IOM ranges and practical tips). (CDC)
IOM/National Academies: Weight Gain During Pregnancy: Reexamining the Guidelines (foundational guideline). (National Academies Press)
ACOG: Weight Gain During Pregnancy & Nutrition During Pregnancy (clinician and patient guidance). (ACOG)
Mayo Clinic: typical distribution of pregnancy weight. (Mayo Clinic)