How much weight to gain in pregnancy depends on your BMI before pregnancy. The Institute of Medicine (IOM) recommends 28 to 40 lb if you were underweight, 25 to 35 lb at a healthy weight, 15 to 25 lb if overweight, and 11 to 20 lb with obesity, for one baby. Most of it comes after the first trimester, at about a pound a week for a healthy-weight start.
Enter your height and pre-pregnancy weight for your range. Add the week and your weight now to see whether your gain so far is on track. The guidelines for twins are included too.
Worked example
Height: 5 ft 5 inWeight before pregnancy: 140 lbWeek of pregnancy: 20 weeksWeight now: 152 lbExpecting: One baby
Recommended total gain: 25–35 lb On track for week 20
A pre-pregnancy weight of 140 lb at 5 ft 5 in is a BMI of 23.3, so the guideline is 25 to 35 lb in total. By week 20 about 7 to 12 lb is expected; a 12 lb gain is at the top of that range.
Open this example in the calculator →How to use the Pregnancy Weight Gain Calculator
- Choose US or metric units and enter your height and your weight before pregnancy.
- Optionally add the week of pregnancy and your weight now.
- Choose one baby or twins.
- Read the recommended total gain, the range for your week and whether you are on track.
Pregnancy weight gain guidelines (IOM 2009)
| BMI before pregnancy | Total gain, one baby | Per week, weeks 14–40 | Total gain, twins |
|---|---|---|---|
| Underweight below 18.5 | 28–40 lb (12.5–18 kg) | 1–1.3 lb (0.44–0.58 kg) | No guideline |
| Healthy 18.5–24.9 | 25–35 lb (11.5–16 kg) | 0.8–1 lb (0.35–0.50 kg) | 37–54 lb (17–25 kg) |
| Overweight 25–29.9 | 15–25 lb (7–11.5 kg) | 0.5–0.7 lb (0.23–0.33 kg) | 31–50 lb (14–23 kg) |
| Obesity 30 or more | 11–20 lb (5–9 kg) | 0.4–0.6 lb (0.17–0.27 kg) | 25–42 lb (11–19 kg) |
The weekly rates assume a gain of 1.1 to 4.4 lb (0.5 to 2 kg) over the first trimester. These guidelines are used by the American College of Obstetricians and Gynecologists and the CDC. The twin figures are the IOM's provisional ranges.
Where the weight goes
For a typical healthy-weight pregnancy, roughly: baby 7 to 8 lb; placenta 1 to 2 lb; amniotic fluid about 2 lb; larger uterus about 2 lb; breast tissue 1 to 3 lb; extra blood about 4 lb; other body fluid 2 to 3 lb; and fat stores 6 to 8 lb, which are used in breastfeeding. Only the last part is fat, which is why BMI is not used during pregnancy.
Why gaining the right amount matters
- Too little is linked with a baby born small for its age and with preterm birth.
- Too much is linked with gestational diabetes, high blood pressure, a large baby, a caesarean birth, and weight that stays on after the birth.
In the United States about half of pregnant women gain more than the guideline. Small changes — regular walking, fewer sugary drinks, and eating to appetite rather than for two — are usually enough to stay in range.
How many extra calories do I need?
None in the first trimester for most people. About 340 extra calories a day in the second trimester and about 450 in the third, for one baby starting at a healthy weight — roughly a sandwich or a yogurt with fruit and nuts, not a second dinner.
How this calculator works
Your pre-pregnancy BMI is your weight before pregnancy divided by your height squared, rounded to one decimal and classified by the WHO cut-offs, as the IOM does. The range for a given week assumes a first-trimester gain of 1.1 to 4.4 lb (0.5 to 2 kg), then rises steadily to the IOM total at 40 weeks. US figures use the IOM's pound ranges and metric figures its kilogram ranges, which the IOM rounded separately.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy: 28–40 lb if underweight, 25–35 lb at a healthy weight, 15–25 lb if overweight and 11–20 lb with obesity, for one baby (IOM 2009).
How much weight should I gain in the first trimester?
About 1 to 4.5 lb (0.5 to 2 kg) in total. Many people gain little or even lose a little because of nausea, which is usually fine; most of the gain comes later.
How much weight should I have gained at 20 weeks?
For someone who started at a healthy weight, about 7 to 12 lb by week 20. Enter your details above for your own range.
How much weight should I gain with twins?
37 to 54 lb at a healthy pre-pregnancy weight, 31 to 50 lb if overweight and 25 to 42 lb with obesity. The IOM gives no twin range for underweight, where a doctor sets the target.
Is it OK to lose weight while pregnant if I am overweight?
Dieting to lose weight during pregnancy is not recommended. With obesity, some doctors accept a gain below the IOM’s 11 lb if the baby is growing well, but that is a decision for your care team.
Can I use a normal BMI calculator while pregnant?
No. Use your weight from before pregnancy: that pre-pregnancy BMI is what the guidelines are based on. BMI during pregnancy includes the baby, placenta and extra fluid.
Sources
- Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines (2009) — National Academies Press
- Obesity and overweight (fact sheet) — World Health Organization
- Adult BMI Categories — Centers for Disease Control and Prevention
For general information only — not a diagnosis or a substitute for advice from a doctor. How we calculate.