How much weight to gain in pregnancy
In 2009 the Institute of Medicine (IOM) and the National Research Council published the weight gain guidelines that the CDC still lists today. They depend on your body mass index (BMI) before pregnancy, using the BMI categories of the World Health Organization. For one baby:
| Pre-pregnancy BMI | Total gain | Weekly gain, 2nd and 3rd trimester |
|---|---|---|
| Underweight below 18.5 | 28 to 40 lb 12.5 to 18 kg | 1 lb (1 to 1.3) 0.51 kg (0.44 to 0.58) |
| Normal weight 18.5 to 24.9 | 25 to 35 lb 11.5 to 16 kg | 1 lb (0.8 to 1) 0.42 kg (0.35 to 0.5) |
| Overweight 25.0 to 29.9 | 15 to 25 lb 7 to 11.5 kg | 0.6 lb (0.5 to 0.7) 0.28 kg (0.23 to 0.33) |
| Obese 30.0 or more | 11 to 20 lb 5 to 9 kg | 0.5 lb (0.4 to 0.6) 0.22 kg (0.17 to 0.27) |
The weekly rates are a mean with a range in brackets. The IOM notes that they assume a gain of 0.5 to 2 kg (1.1 to 4.4 lb) in the first trimester. In the IOM table the obese group covers every BMI of 30.0 or more.
Weight gain with twins
For twins the IOM gives provisional total ranges at term, based on women who gave birth to twins at 37 to 42 weeks with babies weighing about 2,500 g or more. It found too little information to set even a provisional range for underweight women, and it gives no weekly rates for twins.
| Pre-pregnancy BMI | Total gain with twins |
|---|---|
| Underweight | no IOM guideline |
| Normal weight | 37 to 54 lb (17 to 25 kg) |
| Overweight | 31 to 50 lb (14 to 23 kg) |
| Obese | 25 to 42 lb (11 to 19 kg) |
The CDC page on weight gain during pregnancy lists 50 to 62 lb for underweight women with twins, and notes that this figure comes from a 2003 study by Luke and others, not from the IOM. The calculator shows it with that note.
How the calculator checks your week
The guideline gives a total and weekly rates, not a chart for every week. To compare your gain with your week, the calculator builds an approximate range from the guideline’s own numbers:
- Weeks 0 to 12: the first-trimester gain of 0.5 to 2 kg, spread evenly over the weeks. At week 6 that is 0.25 to 1 kg. The Office on Women’s Health counts the first trimester as week 1 to week 12.
- After week 12: 0.5 kg plus the low weekly rate for each week, up to 2 kg plus the high weekly rate for each week.
High = 2 kg + high rate × (w − 12)
With a normal weight BMI at week 24, that is 0.5 + 0.35 × 12 = 4.7 kg up to 2 + 0.50 × 12 = 8 kg, or 10.4 to 17.6 lb. The calculator works in kilograms, as the guideline’s rates are given most precisely there, and converts to pounds.
| Week | Underweight | Normal weight | Overweight | Obese |
|---|---|---|---|---|
| 8 | 0.7 to 2.9 lb 0.3 to 1.3 kg | 0.7 to 2.9 lb 0.3 to 1.3 kg | 0.7 to 2.9 lb 0.3 to 1.3 kg | 0.7 to 2.9 lb 0.3 to 1.3 kg |
| 12 | 1.1 to 4.4 lb 0.5 to 2 kg | 1.1 to 4.4 lb 0.5 to 2 kg | 1.1 to 4.4 lb 0.5 to 2 kg | 1.1 to 4.4 lb 0.5 to 2 kg |
| 16 | 5 to 9.5 lb 2.3 to 4.3 kg | 4.2 to 8.8 lb 1.9 to 4 kg | 3.1 to 7.3 lb 1.4 to 3.3 kg | 2.6 to 6.8 lb 1.2 to 3.1 kg |
| 20 | 8.9 to 14.6 lb 4 to 6.6 kg | 7.3 to 13.2 lb 3.3 to 6 kg | 5.2 to 10.2 lb 2.3 to 4.6 kg | 4.1 to 9.2 lb 1.9 to 4.2 kg |
| 24 | 12.7 to 19.8 lb 5.8 to 9 kg | 10.4 to 17.6 lb 4.7 to 8 kg | 7.2 to 13.1 lb 3.3 to 6 kg | 5.6 to 11.6 lb 2.5 to 5.2 kg |
| 28 | 16.6 to 24.9 lb 7.5 to 11.3 kg | 13.4 to 22 lb 6.1 to 10 kg | 9.2 to 16 lb 4.2 to 7.3 kg | 7.1 to 13.9 lb 3.2 to 6.3 kg |
| 32 | 20.5 to 30 lb 9.3 to 13.6 kg | 16.5 to 26.5 lb 7.5 to 12 kg | 11.2 to 19 lb 5.1 to 8.6 kg | 8.6 to 16.3 lb 3.9 to 7.4 kg |
| 36 | 24.4 to 35.1 lb 11.1 to 15.9 kg | 19.6 to 30.9 lb 8.9 to 14 kg | 13.3 to 21.9 lb 6 to 9.9 kg | 10.1 to 18.7 lb 4.6 to 8.5 kg |
| 40 | 28.3 to 40.2 lb 12.8 to 18.2 kg | 22.7 to 35.3 lb 10.3 to 16 kg | 15.3 to 24.8 lb 6.9 to 11.2 kg | 11.6 to 21.1 lb 5.3 to 9.6 kg |
This is an approximation. Real weight gain is not a straight line, and the weekly rates do not add up exactly to the total range: at week 40 the method gives 12.8 to 18.2 kg for underweight, 10.3 to 16 kg for normal weight, 6.9 to 11.2 kg for overweight, 5.3 to 9.6 kg for obese, close to but not the same as the totals in the first table. Use it as a rough guide between visits, not as a target.
Pre-pregnancy BMI
Use your weight before pregnancy. The calculator shows the BMI with one decimal and picks the category from that shown value, so a BMI of 24.96 shows as 25.0 and counts as overweight. For more on BMI itself, see the BMI calculator.
Talk to your prenatal care provider
The guidelines describe ranges for groups of people. Your provider may suggest a different goal because of your health, your age, your pregnancy or how your weight has changed so far. If your gain is above or below the range for your week, bring it up at your next visit rather than changing how you eat on your own. This calculator is for information only and is not medical advice. To plan around the dates, the due date calculator shows your week, trimester and due date, and the ovulation calculator estimates a fertile window.
How to use the pregnancy weight gain calculator
- 1Choose pounds and feet or kilograms and centimeters, and one baby or twins.
- 2Enter your height and your weight before pregnancy to see your BMI, its category and the recommended total gain.
- 3For one baby, add the week of pregnancy and your weight now to see your gain so far and the approximate range for that week on the chart.
- 4Copy the result to take to your next prenatal visit, or copy a link to it.
Sources
- Summary, in Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines, The National Academies Press, 2009, doi:10.17226/12584. Summary chapter: Table S-1 (total gain and weekly rates, first-trimester assumption) and the provisional twin ranges under “Women with Multiple Fetuses”.
- Weight Gain During Pregnancy, Centers for Disease Control and Prevention. Recommendations for one baby and twins, and the underweight twin range from Luke and others, 2003.
- Stages of pregnancy, Office on Women’s Health, U.S. Department of Health and Human Services. Trimesters by week.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. For one baby, the Institute of Medicine guidelines recommend 28 to 40 lb (12.5 to 18 kg) with a BMI below 18.5, 25 to 35 lb (11.5 to 16 kg) with a BMI of 18.5 to 24.9, 15 to 25 lb (7 to 11.5 kg) with a BMI of 25.0 to 29.9 and 11 to 20 lb (5 to 9 kg) with a BMI of 30 or more. Your prenatal care provider may set a different goal for you.
How much weight should I gain with twins?
The Institute of Medicine gives provisional ranges for twins: 37 to 54 lb (17 to 25 kg) with a normal weight BMI, 31 to 50 lb (14 to 23 kg) when overweight and 25 to 42 lb (11 to 19 kg) with obesity. It found too little information for underweight women with twins. The CDC lists 50 to 62 lb for that group, from a separate 2003 study.
How much weight should I gain in the first trimester?
The guideline’s weekly rates assume a gain of 0.5 to 2 kg, about 1.1 to 4.4 lb, in the first trimester. The guideline gives this total, not a weekly rate for the first trimester.
How much weight should I gain per week in the second and third trimester?
For one baby the guideline gives these weekly rates: about 1 lb (0.44 to 0.58 kg) with a BMI below 18.5, about 1 lb (0.35 to 0.50 kg) with a BMI of 18.5 to 24.9, about 0.6 lb (0.23 to 0.33 kg) with a BMI of 25.0 to 29.9 and about 0.5 lb (0.17 to 0.27 kg) with a BMI of 30 or more. There are no weekly rates for twins.
Which weight do I use for my BMI?
Your weight before pregnancy, with your height. The recommendations are based on pre-pregnancy BMI, so a weight from later in pregnancy would put you in the wrong group. If you are not sure of your weight before pregnancy, ask your prenatal care provider what they have on record.
What if my gain is outside the range for my week?
Talk to your prenatal care provider. The week-by-week range here is an estimate built from the guideline’s first-trimester total and weekly rates, weight changes from day to day, and your provider knows your health and your pregnancy. This calculator is for information only and is not medical advice.
Is my data sent anywhere?
No. The calculation runs in your browser and nothing is stored or sent. If you copy a share link, your height, weights and week are part of that link, so share it only where you want them seen.