Last updated: March 2026
How Much Weight Should You Gain During Pregnancy?
Healthy weight gain during pregnancy depends primarily on your pre-pregnancy Body Mass Index (BMI). The Institute of Medicine published comprehensive guidelines in 2009 that remain the standard recommendation used by healthcare providers today.
For women with a normal BMI (18.5-24.9), the recommended total weight gain is 25-35 pounds over the full 40 weeks. Underweight women are encouraged to gain slightly more (28-40 lbs) to ensure adequate nutrition for the baby, while overweight and obese women are advised to gain less (15-25 lbs and 11-20 lbs, respectively) to reduce complications.
The pattern of gain matters as much as the total. First trimester gain is typically minimal — just 1-4 pounds total — as the baby is still very small. The second and third trimesters see steady gain at about 0.5-1 pound per week, depending on your BMI category. This is when the baby grows most rapidly and your body builds up reserves for breastfeeding.
Understanding Your Weight Gain Results
The calculator shows a green recommended band on the weight gain chart. This represents the healthy range for your BMI category at each week of pregnancy. Your actual weight gain is plotted as a blue line.
Being slightly above or below the band at any given week is completely normal. What matters more is the overall trend over time. Weight can fluctuate daily by several pounds due to water retention, meals, and other factors that have nothing to do with actual fat or tissue gain.
If you're consistently tracking well outside the recommended range, that's worth discussing with your healthcare provider. They may adjust dietary guidance or investigate whether there are any underlying factors. Remember, these are population-level guidelines — your individual needs may differ based on your health history, activity level, and other factors.
Frequently Asked Questions
How much weight should I gain during pregnancy?
It depends on your pre-pregnancy BMI. The Institute of Medicine recommends 25-35 lbs for normal weight (BMI 18.5-24.9), 28-40 lbs for underweight (BMI <18.5), 15-25 lbs for overweight (BMI 25-29.9), and 11-20 lbs for obese (BMI 30+). For twins, add 10-15 lbs to these ranges.
When does most pregnancy weight gain happen?
Most weight gain occurs in the second and third trimesters. During the first trimester (weeks 1-12), you might gain only 1-4 lbs total. After that, steady gain of about 0.5-1 lb per week is typical, depending on your BMI category.
What if I'm gaining too much or too little weight?
Don't panic — the IOM ranges are guidelines, not strict rules. Small deviations are normal. However, consistently gaining well above or below the recommended range can increase certain pregnancy risks. Talk to your healthcare provider, who can give you personalized guidance based on your specific situation.
Is the weight gain recommendation different for twins?
Yes. The IOM recommends about 37-54 lbs for normal weight mothers carrying twins, 31-50 lbs for overweight, and 25-42 lbs for obese. This tool adds 10-15 lbs to the singleton ranges when the twins toggle is enabled.
Where does pregnancy weight gain go?
At full term, the baby accounts for about 7-8 lbs, the placenta 1-2 lbs, amniotic fluid 2 lbs, uterus growth 2 lbs, increased blood volume 3-4 lbs, breast tissue 1-2 lbs, and additional fat/nutrient stores 6-8 lbs. The total adds up to the recommended 25-35 lbs for normal weight women.