The Pregnancy Weight Gain Calculator computes the recommended total and week-by-week gestational weight gain trajectory based on your pre-pregnancy BMI, gestational week, and singleton vs. twins status according to the official Institute of Medicine (IOM) standards.
• Select your Measurement System (US Imperial vs. Metric Units).
• Select your current Gestational Stage (Week 1–40+) and whether you are pregnant with Twins.
• Enter your Height, Pre-Pregnancy Weight, and Current Weight.
• Click Calculate to inspect your pre-pregnancy BMI category, healthy week-by-week trajectory graph, and anatomical weight distribution breakdown.
Equivalent: 165 cm
Equivalent: 61.2 kg
Equivalent: 65.8 kg
Your weight gain is right inside the healthy IOM recommended target range for Week 20 (6.6 – 11.5 lbs).
Category range: 18.5 – 24.9 BMI
Expected weight: 141.6 – 146.5 lbs
Total gain through Week 40
1st trimester total: 1–4.5 lbs
Corridor illustrates the shaded target zone across 40 weeks of gestation for a pre-pregnancy BMI of 22.5 (Normal Weight).
Understanding the maternal and fetal biological components making up an average ~30 lb (13.6 kg) weight gain.
Average full-term infant birth weight
Energy reserves for fetal development & lactation
50% surge in circulatory blood supply
Hydration and tissue fluid support
Protective fluid surrounding the baby
Uterine myometrial muscle hypertrophy
Glandular development preparing for breastfeeding
Nutrient and oxygen delivery organ
Standard weight gain standards recommended by the Institute of Medicine and American College of Obstetricians and Gynecologists.
| Pre-Pregnancy BMI Category | BMI Range (kg/m²) | Singleton Total Gain (lbs) | Singleton Total Gain (kg) | 2nd/3rd Tri Rate (lb/wk) | Twins Total Gain (lbs) |
|---|---|---|---|---|---|
| Underweight | < 18.5 | 28 – 40 lbs | 12.5 – 18.0 kg | 1.0 – 1.3 lb/wk | 50 – 62 lbs (23–28 kg) |
| Normal Weight (Standard) | 18.5 – 24.9 | 25 – 35 lbs | 11.5 – 16.0 kg | 0.8 – 1.0 lb/wk | 37 – 54 lbs (17–25 kg) |
| Overweight | 25.0 – 29.9 | 15 – 25 lbs | 7.0 – 11.5 kg | 0.5 – 0.7 lb/wk | 31 – 50 lbs (14–23 kg) |
| Obese (Class I, II, III) | ≥ 30.0 | 11 – 20 lbs | 5.0 – 9.0 kg | 0.4 – 0.6 lb/wk | 25 – 42 lbs (11–19 kg) |
In 2009, the Institute of Medicine (IOM), in partnership with the National Research Council (NRC), revised gestational weight gain standards to optimize maternal and fetal outcomes. Rather than prescribing a uniform "one-size-fits-all" weight gain target, the guidelines calibrate weight recommendations specifically to a woman's pre-pregnancy Body Mass Index (BMI).
A woman entering pregnancy underweight has lower baseline nutrient and adipose reserves, necessitating greater gestational weight gain to protect against low birth weight and preterm delivery. Conversely, women entering pregnancy in overweight or obese BMI categories already have substantial energy reserves and require fewer surplus calories.
During the first trimester (Weeks 1–13), fetal growth is rapid in cellular differentiation but small in total mass (the embryo weighs ~1 ounce by week 13). Therefore, recommended first-trimester weight gain is modest (1 to 4.5 lbs total). From week 14 onward, maternal plasma expansion, placenta enlargement, and fetal tissue acceleration require steady weekly gains (~0.8 to 1.0 lb/week).
Medical Disclaimer: This calculator provides general weight gain estimations based on the Institute of Medicine (IOM) 2009 guidelines for singleton and twin gestations. It is intended for educational purposes only and does not replace individualized prenatal medical advice, clinical diagnoses, or direct supervision by your obstetrician, certified nurse-midwife, or maternal-fetal medicine specialist.