Pregnancy Weight Gain Calculator

1. Enter your pre-pregnancy weight. Use your weight from before you became pregnant or from your first prenatal visit, whichever is closer to your pre-conception weight.
2. Enter your height. This is used to calculate your pre-pregnancy BMI, which determines which IOM guideline applies to you.
3. Enter your current pregnancy week. This lets the calculator estimate how much weight you should have gained so far.
4. Select the number of babies. Twin and multiple pregnancies have higher weight gain recommendations.
5. Compare your results to the guidelines. The calculator shows both the total recommended gain and how much you should have gained at your current week.

The Institute of Medicine (IOM) 2009 guidelines use pre-pregnancy BMI to set total weight gain targets. BMI is calculated the standard way:

BMI = weight (kg) / height (m)²

Then IOM guidelines assign a total weight gain range based on BMI category:

Weight gain is not distributed evenly across pregnancy. Most women gain 1-4 lbs in the first trimester and then about 0.5-1 lb per week in the second and third trimesters. The calculator applies this distribution curve to estimate expected gain at any given week.