Pregnancy Weight Gain Calculator

Tracking weight gain week by week, measured against your pre-pregnancy Body Mass Index (BMI), gives a clearer read on a pregnancy than a single end-of-term total. The tool maps recommended gain across the weeks using the Institute of Medicine's 2009 guidelines, supporting healthy development for the baby and steady well-being for the mother.

The recommendations come from the Institute of Medicine (IOM) guidelines, which set different target ranges depending on whether pre-pregnancy BMI falls in the underweight, normal weight, overweight, or obese category. The calculator spreads that total over 40 weeks: 10% of it by the end of week 12, then an even weekly pace to week 40. The IOM report itself assumes 1.1-4.4 pounds in the first trimester and sets second- and third-trimester rates of about 1 pound a week for normal weight (0.8-1), 1-1.3 for underweight, 0.5-0.7 for overweight and 0.4-0.6 for obese. A Twins option switches to the IOM's provisional twin ranges: 37-54 pounds for normal weight, 31-50 for overweight and 25-42 for obese (the IOM found too little data to set one for underweight women).

These figures are guidelines rather than rules, and what is right for you can differ, so your healthcare provider remains the best source for advice tailored to your pregnancy. Watching only the final total while ignoring the weekly trajectory tends to breed either needless worry or unhealthy shortcuts, when the gradual progression is what the guidance is really about.