Pregnancy Weight Gain Calculator
Find out how much weight you should gain during pregnancy based on your pre-pregnancy BMI. Our calculator uses the Institute of Medicine (IOM) guidelines to provide personalized recommendations by trimester.
How the Weight Gain Calculator Works
Step 1: BMI Calculation
The calculator first determines your pre-pregnancy Body Mass Index (BMI) using your height and weight. BMI is calculated as weight in kilograms divided by height in meters squared (or weight in pounds divided by height in inches squared, multiplied by 703).
Step 2: IOM Category Assignment
Your BMI places you in one of four categories:
- Underweight (BMI under 18.5): 28-40 lbs total gain recommended
- Normal Weight (BMI 18.5-24.9): 25-35 lbs total gain recommended
- Overweight (BMI 25-29.9): 15-25 lbs total gain recommended
- Obese (BMI 30 or higher): 11-20 lbs total gain recommended
Step 3: Trimester Breakdown
During the first trimester (weeks 1-13), a modest gain of 1-4.4 pounds is typical for all BMI categories. In the second and third trimesters, the recommended weekly rate of gain varies by BMI category, reflecting different caloric and nutritional needs.
Frequently Asked Questions
How much weight should I gain during pregnancy?▾
Recommended weight gain depends on your pre-pregnancy BMI. Underweight women (BMI < 18.5) should gain 28-40 lbs, normal weight (BMI 18.5-24.9) should gain 25-35 lbs, overweight (BMI 25-29.9) should gain 15-25 lbs, and obese women (BMI 30+) should gain 11-20 lbs, according to IOM guidelines.
What are the IOM weight gain guidelines?▾
The Institute of Medicine (IOM, now the National Academy of Medicine) published evidence-based guidelines for pregnancy weight gain in 2009. These recommendations are based on pre-pregnancy BMI and are endorsed by ACOG and most healthcare organizations worldwide.
When does most pregnancy weight gain occur?▾
Most weight gain occurs in the second and third trimesters. During the first trimester, only 1-4.4 pounds of gain is typical. After that, steady weekly gain is expected, with the rate depending on your BMI category.
Is it harmful to gain too much or too little weight during pregnancy?▾
Yes. Gaining too little can increase the risk of preterm birth and low birth weight. Gaining too much is associated with gestational diabetes, preeclampsia, cesarean delivery, and postpartum weight retention. Following the IOM guidelines helps optimize outcomes for both mother and baby.
Does the recommended weight gain change for twins?▾
Yes. For twin pregnancies, the IOM recommends higher weight gain: normal weight women should gain 37-54 lbs, overweight women 31-50 lbs, and obese women 25-42 lbs. This calculator is designed for singleton pregnancies. Consult your provider for multiple pregnancy guidance.
Medical Disclaimer
This calculator is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider for medical decisions regarding your pregnancy.