Pregnancy Weight Gain Calculator
Enter your pre-pregnancy height and weight to see the recommended weight gain range for a healthy pregnancy by trimester.
Reviewed by the ToolNestr Editorial Team — July 2026
Enter your height and pre-pregnancy weight.
About pregnancy weight gain
Healthy weight gain during pregnancy supports your baby's growth and development while maintaining your own health. The American College of Obstetricians and Gynecologists recommends weight gain ranges based on your pre-pregnancy BMI. Gaining too little or too much can increase risks for both mother and baby. This calculator follows the Institute of Medicine (IOM) guidelines published in 2009, which remain the standard in obstetrics. For context on your pre-pregnancy health, check your BMI and Calorie Calculator.
For informational purposes only. Follow your healthcare provider's specific recommendations.
How it works
The calculator determines your pre-pregnancy BMI from your height and weight, then applies the IOM guidelines to find your recommended total weight gain range. It also shows the expected gain by your current week of pregnancy. The IOM guidelines are based on large observational studies and are designed to optimise outcomes for both mother and baby. Gaining within the recommended range reduces the risk of gestational diabetes, preeclampsia, C-section delivery, preterm birth and postpartum weight retention.
The guidelines explained
IOM weight gain recommendations by pre-pregnancy BMI:
Underweight (BMI < 18.5): 12.5–18 kg (28–40 lb)
Normal (BMI 18.5–24.9): 11.5–16 kg (25–35 lb)
Overweight (BMI 25–29.9): 7–11.5 kg (15–25 lb)
Obese (BMI 30+): 5–9 kg (11–20 lb)
Worked example
A woman is 165 cm tall and weighed 58 kg before pregnancy. She is currently 24 weeks pregnant. What should her target be?
Expectant mother
Track your weight gain against the recommended range for your BMI to ensure you and your baby are on track for a healthy pregnancy.
Midwife
Quickly calculate the recommended weight gain range for patients to discuss during prenatal visits and track progress over time.
Dietitian
Use the BMI-based ranges to counsel pregnant clients on appropriate weight gain and provide tailored nutrition advice for each trimester.
Birth educator
Teach expectant parents what healthy weight gain looks like and why the range varies based on starting BMI.
How to use this calculator
Enter pre-pregnancy stats
Provide your height and weight from before pregnancy. These determine your starting BMI category.
Select current week
Choose how many weeks pregnant you are now. The calculator shows how much gain is expected by this point.
Read your range
See your recommended total gain range, your BMI category and the expected gain by your current week. Use this as a general guide.
Tips for healthy pregnancy weight
Eat nutrient-dense foods
Focus on whole foods that provide protein, healthy fats, fibre, vitamins and minerals. Your calorie needs increase by roughly 300–450 per day in the second and third trimesters.
Stay active
Moderate exercise during pregnancy is safe and beneficial for most women. Walking, swimming and prenatal yoga help manage weight gain and improve outcomes.
Hydrate well
Proper hydration supports increased blood volume, amniotic fluid and nutrient transport. Aim for 8–10 glasses of water per day during pregnancy.
Related tools
Frequently asked questions
How much weight should I gain during pregnancy?
The recommended total weight gain depends on your pre-pregnancy BMI: underweight (BMI < 18.5): 12.5–18 kg. Normal weight (BMI 18.5–24.9): 11.5–16 kg. Overweight (BMI 25–29.9): 7–11.5 kg. Obese (BMI 30+): 5–9 kg.
How does weight gain distribute across trimesters?
First trimester: 0.5–2 kg total (minimal). Second trimester: ~0.45–0.6 kg per week. Third trimester: ~0.35–0.5 kg per week. The majority of gain happens in the second half of pregnancy.
Where does the extra weight go?
Average weight gain breaks down as: baby ~3.4 kg, placenta ~0.7 kg, amniotic fluid ~0.9 kg, uterine tissue ~1 kg, breast tissue ~0.5 kg, blood volume ~1.5 kg, and maternal fat stores ~2.5 kg.
Can I lose weight during pregnancy?
Weight loss during pregnancy is generally not recommended and may harm the baby. If you are overweight, your provider may recommend minimal weight gain, but not active weight loss.
What if I gain too much or too little?
Gaining too little increases the risk of low birth weight. Gaining too much increases the risk of gestational diabetes, preeclampsia, C-section and postpartum weight retention. Aim for the middle of your recommended range.