Pregnancy Body Changes Calculator
See the recommended weight gain for your week of pregnancy and pre-pregnancy BMI (Institute of Medicine 2009 guidelines), with the trimester and the fundal height a clinician would expect.
Last updated: October 2026
Recommended weight gain so far (middle of the range)
13.55 lb
Formula below · 4 sources (ncbi.nlm.nih.gov, CDC, womenshealth.gov, my.clevelandclinic.org) · Updated Oct 2026
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About this calculator
Weight gain and the growing bump are the two body changes clinicians track week by week. This calculator works out how much weight the Institute of Medicine (IOM) 2009 guidelines, which the CDC uses, would expect you to have gained by your current week, based on your BMI before pregnancy.
How the range is built
The IOM assumes a gain of 1.1 to 4.4 lb (0.5 to 2 kg) over the first trimester, for every BMI group. From week 14 on, it gives a steady weekly rate that depends on BMI: 1 to 1.3 lb a week if you were underweight, 0.8 to 1 lb with a healthy weight, 0.5 to 0.7 lb if overweight and 0.4 to 0.6 lb with obesity. The calculator spreads the first-trimester gain evenly over weeks 1 to 13, adds the weekly rate after that, and shows the middle of the range as the result. The chart shows the low and high ends of the range for every week.
Because the weekly rates are rounded, the range at week 40 is close to, but not exactly, the IOM total for the whole pregnancy (25 to 35 lb for a healthy weight, for example). The table below lists the totals.
The bump: fundal height
At prenatal visits from about 20 weeks, clinicians measure fundal height, the distance from the pubic bone to the top of the uterus. In centimeters it roughly equals the week of pregnancy, give or take 2 cm: about 28 cm at 28 weeks. Waist size has no clinical standard, so it is not used to judge how a pregnancy is going.
This is an estimate for planning, not medical advice. Twins, a very low or high starting weight and some health conditions change the targets, so ask your clinician for yours.
| Pre-pregnancy BMI | Total, one baby | Per week, 2nd and 3rd trimesters | Total, twins |
|---|---|---|---|
| Underweight (under 18.5) | 28–40 lb | 1–1.3 lb | 50–62 lb |
| Healthy weight (18.5–24.9) | 25–35 lb | 0.8–1 lb | 37–54 lb |
| Overweight (25.0–29.9) | 15–25 lb | 0.5–0.7 lb | 31–50 lb |
| Obesity (30.0 and above) | 11–20 lb | 0.4–0.6 lb | 25–42 lb |
How to use
Enter the current week of pregnancy and pick your BMI category from before you were pregnant. Example (the defaults): at week 25 with a healthy pre-pregnancy BMI, the low end is 1.1 + (25 − 13) × 0.8 = 10.7 lb and the high end is 4.4 + (25 − 13) × 1.0 = 16.4 lb. The calculator shows the midpoint, 13.55 lb, so a gain of roughly 11 to 16 lb so far is on track. At week 30 with a pre-pregnancy BMI in the overweight range, the range is 9.6 to 16.3 lb and the midpoint is 12.95 lb. At week 10 any BMI group gives 0.85 to 3.4 lb.
Frequently asked questions
How much weight should I gain during pregnancy in total?
For one baby, the IOM and CDC recommend 28 to 40 lb if you were underweight before pregnancy (BMI under 18.5), 25 to 35 lb with a healthy weight, 15 to 25 lb if overweight and 11 to 20 lb with obesity. The ranges are higher for twins (see the table).
I have gained more or less than this range. Is something wrong?
Not necessarily. Weight changes from week to week with fluid, nausea in early pregnancy and when you weigh yourself. The range is a guide your clinician uses over several visits. Tell them if you gain or lose weight suddenly, or if you notice swelling of the face or hands.
What is fundal height?
The distance from the pubic bone to the top of the uterus, measured with a tape at prenatal visits. From about 20 weeks it roughly equals the number of weeks of pregnancy in centimeters, plus or minus 2 cm. A measurement well outside that range can lead to an ultrasound to check the baby's growth and the fluid around it.
When does the bump start to show?
Usually in the second trimester (weeks 13 to 28), as the uterus rises out of the pelvis. It often shows earlier in a second pregnancy. Around week 20 the top of the uterus is near the navel.
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