Pregnancy weight gain calculator
This pregnancy weight gain calculator uses your weight before pregnancy and your height to work out your body mass index (BMI), then shows the total weight gain range the US Institute of Medicine (IOM) recommends for that BMI, for one baby or twins.
Recommended weight gain falls as pre-pregnancy BMI rises
The IOM ranges for total weight gain during pregnancy, by body mass index (BMI) before pregnancy.
| Pre-pregnancy BMI | One baby | Twins |
|---|---|---|
| Underweight BMI below 18.5 | 28–40 lb | No guideline |
| Normal weight BMI 18.5–24.9 | 25–35 lb | 37–54 lb |
| Overweight BMI 25.0–29.9 | 15–25 lb | 31–50 lb |
| Obese BMI 30.0 or more | 11–20 lb | 25–42 lb |
Sources: Institute of Medicine and National Research Council, Weight Gain During Pregnancy: Reexamining the Guidelines (2009), Table S-1; Institute of Medicine and National Research Council (2009), provisional guidelines for twin pregnancy; kilograms as given in ACOG Committee Opinion 548 (2013).
Weight gained in pregnancy has several components
Weight gain during pregnancy includes the baby, the placenta, amniotic fluid, the increase in blood volume, breast tissue and body fat. Each varies between people, the weight of the baby in particular (NICE NG247, 2025).
Evidence for a week-by-week weight gain target is limited
A pregnancy weight gain calculator by week, or a tracker that plots each week against a chart, assumes there is an optimal gain for each stage of pregnancy. NICE notes a lack of evidence on what the optimal gain in each trimester should be (NG247, 2025). The IOM ranges on this page are totals for the whole pregnancy.
Twin pregnancy weight gain ranges are provisional
The IOM could not analyze twin pregnancies as fully as pregnancies with one baby, so it set provisional ranges. They reflect the middle half (the 25th to 75th percentiles) of weight gain among women who gave birth at 37 to 42 weeks to twins weighing 2,500 g or more on average. The IOM found too little information to set a range for twin pregnancies in its underweight category, and the evidence was insufficient for triplets or more (IOM, 2009; ACOG Committee Opinion 548, 2013).
NHS antenatal care does not set weight gain targets
NHS antenatal care in England follows NICE guidance. NICE recommends offering to measure height and weight, and to calculate BMI, at the first antenatal appointment (NG201, 2021). It does not recommend routine weighing through pregnancy without a clinical reason, such as gestational diabetes, and it has set no UK ranges of its own. For anyone who wants to monitor their weight change in a pregnancy with one baby, NICE refers to the IOM ranges (NG247, 2025).
Intentional weight loss during pregnancy is not recommended
NICE advises that intentional weight loss during pregnancy is not recommended, because of potential adverse effects on the baby (NG247, 2025). Questions about weight in your own pregnancy are for your midwife or doctor, who can take your circumstances into account.
Sources
- National Institute for Health and Care Excellence. Maternal and child nutrition: nutrition and weight management in pregnancy, and nutrition in children up to 5 years (NG247). 2025.
- National Institute for Health and Care Excellence. Antenatal care (NG201). Published 19 August 2021; last reviewed 27 December 2024.
- Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press; 2009. doi:10.17226/12584.
- American College of Obstetricians and Gynecologists. Weight gain during pregnancy (Committee Opinion No. 548). Obstetrics & Gynecology. 2013;121(1):210–212. doi:10.1097/01.AOG.0000425668.87506.4c.