Pregnancy
Pregnancy weight gain calculator and chart by week
Enter your weight before pregnancy, your height and how many weeks pregnant you are. The calculator works out your pre-pregnancy BMI and shows the total weight gain the Institute of Medicine (IOM) recommends for it, plus the range that is typical by your current week. These are ranges to discuss with your midwife or doctor, who know how your pregnancy is going.
Enter your values above to see your result and what it means.
How much weight should I gain during pregnancy?
The Institute of Medicine (2009) recommends a total gain that depends on your BMI before pregnancy: 12.5-18 kg (28-40 lb) for a BMI under 18.5, 11.5-16 kg (25-35 lb) for 18.5-24.9, 7-11.5 kg (15-25 lb) for 25-29.9 and 5-9 kg (11-20 lb) for 30 or more. The American College of Obstetricians and Gynecologists adopted these ranges in Committee Opinion 548. Twins have higher, provisional ranges.
| Pre-pregnancy BMI | Total, one baby | Weekly, 2nd and 3rd trimester | Total, twins (provisional) |
|---|---|---|---|
| Under 18.5 | 28-40 lb (12.5-18 kg) | 1-1.3 lb (0.44-0.58 kg) | No guideline (insufficient data) |
| 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) |
| 25.0-29.9 | 15-25 lb (7-11.5 kg) | 0.5-0.7 lb (0.23-0.33 kg) | 31-50 lb (14-23 kg) |
| 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) |
Pregnancy weight gain chart by week
The IOM table assumes 1.1-4.4 lb (0.5-2 kg) in the first trimester and then a steady weekly gain. Adding the weekly range to that first-trimester figure gives the typical cumulative gain below, for one baby. The calculator uses the same arithmetic for any week you enter. Real gain is uneven, so treat each figure as a band around a trend.
| Week | BMI under 18.5 | BMI 18.5-24.9 | BMI 25-29.9 | BMI 30 or more |
|---|---|---|---|---|
| 13 | 1.1-4.4 lb | 1.1-4.4 lb | 1.1-4.4 lb | 1.1-4.4 lb |
| 20 | 8.1-13.5 lb | 6.7-11.4 lb | 4.6-9.3 lb | 3.9-8.6 lb |
| 24 | 12.1-18.7 lb | 9.9-15.4 lb | 6.6-12.1 lb | 5.5-11 lb |
| 28 | 16.1-23.9 lb | 13.1-19.4 lb | 8.6-14.9 lb | 7.1-13.4 lb |
| 32 | 20.1-29.1 lb | 16.3-23.4 lb | 10.6-17.7 lb | 8.7-15.8 lb |
| 36 | 24.1-34.3 lb | 19.5-27.4 lb | 12.6-20.5 lb | 10.3-18.2 lb |
| 40 | 28.1-39.5 lb | 22.7-31.4 lb | 14.6-23.3 lb | 11.9-20.6 lb |
Why the range depends on BMI before pregnancy
The IOM committee reviewed how weight gain related to outcomes for mothers and babies, from birth weight to weight kept after the birth, and set a separate range for each WHO BMI category. Your BMI before pregnancy is therefore what the calculator uses; your current weight is not needed and is not judged. If you are unsure of your pre-pregnancy weight, ask your midwife or doctor: ACOG asks clinicians to determine BMI at the first prenatal visit.
What this calculator cannot tell you
It shows population ranges. It cannot see how your baby is growing, how you are feeling, or any condition that changes the picture, and it uses the adult BMI categories. Decisions about weight in pregnancy belong with your midwife or doctor.
Frequently asked questions
How much weight should I gain in pregnancy with a normal BMI?
With a pre-pregnancy BMI of 18.5 to 24.9, the IOM recommends 25 to 35 lb (11.5 to 16 kg) for one baby, usually 1.1 to 4.4 lb in the first trimester and about 0.8 to 1 lb a week after that.
How much weight should I gain in the first trimester?
The IOM recommendations assume 0.5 to 2 kg (1.1 to 4.4 lb) over the whole first trimester, whatever your BMI. If nausea makes eating hard, mention it to your midwife or doctor.
How much weight should I gain with twins?
The IOM gives provisional totals for twins at 37 to 42 weeks: 37 to 54 lb (17 to 25 kg) with a normal pre-pregnancy BMI, 31 to 50 lb (14 to 23 kg) with overweight and 25 to 42 lb (11 to 19 kg) with obesity. There was not enough data to set a range for an underweight BMI.
What if I gain less than the range?
Talk to your midwife or doctor, who will look at how your baby is growing. ACOG notes that individualized care and clinical judgement are needed when someone with overweight or obesity gains less than recommended but has a baby who is growing appropriately.
Where do the weight gain ranges come from?
From the 2009 Institute of Medicine report "Weight Gain During Pregnancy: Reexamining the Guidelines", which ACOG endorsed in Committee Opinion 548. The calculator uses that report's Table S-1 and its provisional twin ranges.
Sources
- Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Rasmussen KM, Yaktine AL, eds. Washington, DC: National Academies Press; 2009 (Summary, Table S-1).
- National Academies Press. Weight Gain During Pregnancy: Reexamining the Guidelines (2009), report page.
- American College of Obstetricians and Gynecologists. Committee Opinion No. 548: Weight gain during pregnancy. Obstet Gynecol. 2013;121(1):210-212.