Pregnancy weight gain calculator.

How the range is worked out

1. BMI before pregnancy = weight (kg) ÷ height (m) squared, put in the WHO category: under 18.5, 18.5 to 24.9, 25 to 29.9, or 30 and over.
2. Total gain for the whole pregnancy (one baby): underweight 28 to 40 lb (12.5 to 18 kg); normal weight 25 to 35 lb (11.5 to 16 kg); overweight 15 to 25 lb (7 to 11.5 kg); obesity 11 to 20 lb (5 to 9 kg).
3. By week: first-trimester gain of 1.1 to 4.4 lb (0.5 to 2 kg), then a weekly rate in the second and third trimesters: underweight 1.0 to 1.3 lb; normal weight 0.8 to 1.0 lb; overweight 0.5 to 0.7 lb; obesity 0.4 to 0.6 lb. The tool adds the first-trimester range (scaled up to week 13) to the weekly rate range for each week after 13.
4. Twins (provisional totals only): normal weight 37 to 54 lb (17 to 25 kg); overweight 31 to 50 lb (14 to 23 kg); obesity 25 to 42 lb (11 to 19 kg). The IOM gave no twin range for underweight.

Worked example. 65 kg, 165 cm gives BMI 23.9 (normal weight). Total 25 to 35 lb. At week 24: 1.1 to 4.4 lb plus 11 weeks at 0.8 to 1.0 lb = about 9.9 to 15.4 lb (4.5 to 7.0 kg).

These are population guidelines for a healthy pregnancy and not personal targets. Your care provider may advise something different. Sources (opened 2026-10-04): Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (National Academies Press, 2009); ACOG Committee Opinion 548, Weight Gain During Pregnancy (2013, reaffirmed).

FAQ

How much weight should I gain in pregnancy?

The IOM range for one baby is 25 to 35 lb (11.5 to 16 kg) if your pre-pregnancy BMI was normal, 28 to 40 lb if underweight, 15 to 25 lb if overweight and 11 to 20 lb with obesity. Your own provider can tailor this.

How much should I gain each week?

After the first trimester the guideline rate is about 1 lb a week for underweight and normal BMI (0.8 to 1.0 for normal weight), 0.5 to 0.7 lb for overweight and 0.4 to 0.6 lb with obesity.

What about twins?

The IOM gave provisional totals of 37 to 54 lb for normal BMI, 31 to 50 lb for overweight and 25 to 42 lb with obesity, and no range for underweight. There is no week-by-week rate here for twins.

Should I use my weight before pregnancy or now?

Use the weight before you were pregnant, as the guidelines are based on pre-pregnancy BMI. If you do not know it, use your earliest recorded weight in pregnancy and treat the result as rough.

I am outside the range. Is something wrong?

Not necessarily. Gain varies a lot between people, and the range is a population guide. Mention it to your midwife or doctor at your next visit rather than dieting or eating more on your own.