Based on the 2009 Institute of Medicine guidelines — the same numbers your OB uses. We'll show you the recommended range, where you are now, and how it tracks week by week.
Right where you should be. To finish in range, aim for about 0.8–1.4 lb per week for the next 20 weeks.
The total-gain ranges (28–40 lb for underweight, 25–35 lb for normal BMI, 15–25 lb for overweight, 11–20 lb for obese) are the 2009 Institute of Medicine / National Academy of Medicine guidelines, reaffirmed by ACOG in 2013 (Committee Opinion 548). They're based on outcomes data linking gestational weight gain to birth weight, cesarean rate, postpartum weight retention, and gestational diabetes risk.
These are population-level guidelines, not a verdict on your body. Some people gain mostly in the second trimester; some catch up in the third. Twin pregnancies have higher recommended ranges (additional ~10 lb on the low end). Hyperemesis, gestational diabetes, and individual metabolism all shift the picture.
The most useful thing you can do with this number is bring it to your OB — they have the rest of the context.
Sources: Institute of Medicine (US) and National Research Council Committee, Weight Gain During Pregnancy: Reexamining the Guidelines (National Academies Press, 2009); ACOG Committee Opinion 548, "Weight Gain During Pregnancy" (2013, reaffirmed 2018).