Find your recommended total and weekly weight gain by pre-pregnancy BMI, based on IOM guidelines.
Estimates only, not medical advice.
This calculator first works out your pre-pregnancy body mass index from the weight and height you enter, then sorts that number into one of four standard categories: underweight, normal, overweight, or obese. Everything else on this page follows from that category.
The Institute of Medicine, whose pregnancy work is now carried on by the National Academies of Sciences, Engineering, and Medicine (NASEM), publishes total and weekly weight gain ranges for each BMI category. This calculator reproduces those published ranges directly.
| Pre-pregnancy BMI category | Total gain, single baby | Weekly gain, 2nd/3rd trimester |
|---|---|---|
| Underweight (BMI under 18.5) | 28 to 40 lb | 1.0 to 1.3 lb |
| Normal (BMI 18.5 to 24.9) | 25 to 35 lb | 0.8 to 1.0 lb |
| Overweight (BMI 25 to 29.9) | 15 to 25 lb | 0.5 to 0.7 lb |
| Obese (BMI 30 and above) | 11 to 20 lb | 0.4 to 0.6 lb |
Carrying twins means growing more placental and fetal tissue overall, so the published guideline ranges shift upward at every BMI category compared with a single baby pregnancy. For a normal pre-pregnancy BMI carrying twins, the range widens to about 37 to 54 pounds total; for overweight, about 31 to 50 pounds; for obese, about 25 to 42 pounds. Because the weekly pace for twin pregnancies varies more than for a single baby, this calculator reports "varies" for the weekly figure in twins mode rather than a single number.
The Institute of Medicine, now part of the National Academies, set separate ranges for each pre pregnancy BMI category because research links total gain to outcomes differently depending on starting weight.
Carrying twins requires more total maternal and fetal tissue growth, so the guideline ranges shift upward across every BMI category compared with a single baby pregnancy.
Weekly pace varies naturally week to week. A single week running high or low is less important than the overall trend, which your provider will track at appointments.
No. Most of the recommended gain happens in the second and third trimesters. First trimester gain is typically much smaller, which is why the weekly figure here describes the later trimesters.