Health
Pregnancy Weight Gain Calculator
Find your recommended total pregnancy weight gain range based on your pre-pregnancy BMI, using official IOM guidelines for singleton and twin pregnancies.
Toggle on for a twin pregnancy
Pre-pregnancy BMI
Recommended Total Weight Gain
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By Trimester
First Trimester (weeks 1–13)
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2nd & 3rd Trimester (approx. weekly rate)
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Note: IOM guidelines do not provide a standardized total weight gain range for underweight women carrying twins — data for this group is insufficient. Work with your healthcare provider to set an individualized target.
Medical disclaimer: This is a general guideline based on Institute of Medicine (IOM) recommendations. It is not medical advice. Always follow your healthcare provider's personalized guidance, since individual health conditions can change your ideal weight gain target.
IOM Guidelines by BMI
| Pre-pregnancy BMI | Singleton | Twins |
|---|---|---|
| Underweight (<18.5) | 28–40 lb | Insufficient data |
| Normal (18.5–24.9) | 25–35 lb | 37–54 lb |
| Overweight (25–29.9) | 15–25 lb | 31–50 lb |
| Obese (≥30.0) | 11–20 lb | 25–42 lb |
Source: Institute of Medicine (2009), "Weight Gain During Pregnancy: Reexamining the Guidelines," adopted by ACOG and the CDC as the standard U.S. reference.
Why BMI matters
Higher starting BMI → lower recommended gain
Women who begin pregnancy with more body reserves need less additional weight to support a healthy pregnancy, so the recommended range shrinks as BMI category rises.
Lower starting BMI → higher recommended gain
Underweight women have fewer reserves and are advised to gain more, reducing the risk of low birth weight and preterm delivery.
Pre-pregnancy BMI = weight (kg) ÷ height² (m). Categories follow standard IOM/WHO thresholds.
Tips for Healthy Gain
First trimester: Gain is typically modest — about 1–4.5 lb total — since the baby is still small and nausea can limit intake.
Second & third trimester: Gain becomes steadier, generally averaging around 0.5–1.3 lb per week depending on BMI category.
Track the trend, not the day: Week-to-week weight naturally fluctuates. Your provider watches the overall trend on a growth chart, not single readings.
Nutrition over restriction: Focus on nutrient-dense foods rather than strict calorie counting. Pregnancy is not the time for intentional weight loss.
FAQ
Frequently asked questions.
How much weight should I gain during pregnancy?
The right amount of weight gain during pregnancy depends on your pre-pregnancy Body Mass Index (BMI), not a single fixed number. The Institute of Medicine (IOM) recommends 28–40 lb for underweight women, 25–35 lb for normal-weight women, 15–25 lb for overweight women, and 11–20 lb for obese women carrying a single baby. Women carrying twins are generally advised to gain more overall. Always confirm your personal target with your OB-GYN or midwife, since individual health conditions can change the recommendation.
What are the IOM pregnancy weight gain guidelines?
The Institute of Medicine (now the National Academy of Medicine) published its most recent pregnancy weight gain guidelines in 2009, based on pre-pregnancy BMI category. They recommend 28–40 lb of total gain for underweight women (BMI under 18.5), 25–35 lb for normal weight (BMI 18.5–24.9), 15–25 lb for overweight (BMI 25–29.9), and 11–20 lb for obese women (BMI 30 and above). These guidelines are widely adopted by the CDC and ACOG as the standard reference used by U.S. healthcare providers.
Is the weight gain recommendation different for twins?
Yes. Women carrying twins are generally advised to gain more total weight than those carrying a single baby, since they are supporting two growing babies, two placentas, and additional fluid. The IOM's twin guidelines suggest about 37–54 lb for normal-weight women, 31–50 lb for overweight women, and 25–42 lb for obese women. There is currently insufficient data to set a firm IOM range for underweight women carrying twins, so this group should work closely with their provider on an individualized target.
Why does the recommended weight gain depend on starting BMI?
Women who start pregnancy at a higher BMI already carry larger energy reserves, so they need less additional weight gain to support a healthy pregnancy and reach a healthy birth weight for the baby. Conversely, women who start underweight have fewer reserves and are advised to gain more to reduce the risk of low birth weight and preterm delivery. This BMI-based, sliding-scale approach aims to optimize outcomes for both mother and baby rather than applying one universal number to everyone.
How is pregnancy weight gain distributed across trimesters?
Most guidelines suggest a modest total gain of roughly 1–4.5 lb during the entire first trimester, since the baby is still very small and morning sickness can limit intake. Weight gain then becomes steadier and more linear through the second and third trimesters, commonly averaging somewhere around 0.5–1.3 lb per week depending on your BMI category. These are general patterns — actual week-to-week gain varies widely between individuals and can fluctuate month to month.
What happens if I gain too much or too little weight during pregnancy?
Gaining significantly more than recommended is associated with a higher risk of gestational diabetes, high blood pressure, a larger-than-average baby, and a more difficult delivery, as well as more postpartum weight to lose. Gaining too little is associated with a higher risk of low birth weight and preterm birth. Both extremes are best managed with regular prenatal checkups, where your provider can track your trend on a growth chart and adjust nutrition or activity guidance as needed.
Last updated: August 17, 2026