Pregnancy Weight Gain Calculator — How Much Weight Should You Gain During Pregnancy?

One of the most common questions expectant mothers ask their healthcare providers is: "How much weight should I gain during pregnancy?" It is a question that matters deeply — both for the health of the growing baby and for the long-term wellbeing of the mother. Gaining too little weight during pregnancy is associated with low birth weight and preterm delivery, while gaining too much is linked to gestational diabetes, hypertension, delivery complications, and difficulty losing weight after birth. Our free Pregnancy Weight Gain Calculator gives you personalised week-by-week guidance based on your pre-pregnancy Body Mass Index, following the official recommendations of the Institute of Medicine (now the National Academy of Medicine), which remain the gold standard used by obstetricians and midwives worldwide.

All calculations in this tool are performed entirely within your browser. Nothing you enter — your weight, height, BMI category, or current week of pregnancy — is sent to any server, stored in any database, or shared with any third party. You can use this calculator as often as you need throughout your pregnancy without any privacy concerns.

Why Pregnancy Weight Gain Guidelines Exist and How They Were Established

The weight gain recommendations used by this calculator come from the 2009 report "Weight Gain During Pregnancy: Reexamining the Guidelines" published by the Institute of Medicine in the United States. This comprehensive review analysed decades of research on maternal and infant outcomes to determine which ranges of gestational weight gain were associated with the best health results for both mother and child. The guidelines were stratified by pre-pregnancy BMI because the relationship between weight gain and health outcomes differs significantly depending on a woman's body composition at the start of pregnancy.

Prior to the IOM guidelines, many clinicians relied on blanket recommendations that did not account for individual variation in pre-pregnancy body weight. The 2009 guidelines corrected this by establishing four distinct ranges based on pre-pregnancy BMI categories, ensuring that underweight women receive guidance to gain more than the average, while women who were overweight or obese before pregnancy receive guidance to gain less. These ranges have been validated by numerous subsequent studies and are endorsed by the American College of Obstetricians and Gynaecologists, the Society of Obstetricians and Gynaecologists of Canada, and health authorities in many other countries.

Recommended Weight Gain Ranges by Pre-Pregnancy BMI

The IOM recommendations for total weight gain during a singleton pregnancy are divided into four categories based on pre-pregnancy BMI:

Underweight (BMI under 18.5): Women who were underweight before pregnancy are recommended to gain between 12.5 and 18 kilograms (28 to 40 pounds) over the course of their pregnancy. The higher recommended range reflects the additional nutritional needs of a body that entered pregnancy with limited reserves. Insufficient weight gain in this category is particularly associated with intrauterine growth restriction and very low birth weight.

Normal weight (BMI 18.5 to 24.9): Women with a pre-pregnancy BMI in the healthy range are advised to gain between 11.5 and 16 kilograms (25 to 35 pounds). This range supports healthy fetal development, adequate amniotic fluid volume, placental growth, and the maternal fat stores needed to support breastfeeding after delivery, while minimising excess fat accumulation that can be difficult to lose postpartum.

Overweight (BMI 25 to 29.9): Women who were overweight before pregnancy are recommended to gain between 7 and 11.5 kilograms (15 to 25 pounds). Staying within this more modest range helps reduce the risk of gestational diabetes, preeclampsia, the need for caesarean delivery, and large-for-gestational-age infants, while still providing sufficient calories and nutrients for healthy fetal development.

Obese (BMI 30 and above): Women with obesity prior to pregnancy are advised to gain between 5 and 9 kilograms (11 to 20 pounds). Despite the lower recommended gain, it is important to understand that no weight loss is recommended during pregnancy — the goal is simply to limit excess accumulation while ensuring that calorie and nutrient needs are fully met through a nutrient-dense diet. Women in this category benefit most from close monitoring by their healthcare team throughout pregnancy.

Twin and Multiple Pregnancies

Women carrying twins or multiples have different weight gain needs than those carrying a single baby. The IOM also provides guidance for twin pregnancies: normal-weight women carrying twins should aim to gain between 17 and 25 kilograms (37 to 54 pounds), overweight women carrying twins should target 14 to 23 kilograms (31 to 50 pounds), and obese women carrying twins are advised to gain between 11 and 19 kilograms (25 to 42 pounds). Our calculator supports both singleton and twin pregnancies and adjusts all recommendations accordingly.

How Weight Gain Is Distributed Across the Three Trimesters

Pregnancy weight gain does not occur at a constant rate. In the first trimester — weeks one through thirteen — total weight gain is typically modest, ranging from roughly 0.5 to 2 kilograms for most women. Many women actually lose a small amount of weight due to morning sickness during this period, and this is generally not a cause for concern provided adequate nutrition is maintained. The second and third trimesters are when the majority of weight gain occurs, with the IOM recommending an average gain of approximately 0.35 to 0.5 kilograms per week for normal-weight women during these periods. Our week-by-week chart makes it easy to track whether your weight gain trajectory is within the expected range at each point in your pregnancy.

Where Does the Pregnancy Weight Go?

A common misconception is that all pregnancy weight gain is simply fat storage. In reality, the additional weight is distributed across multiple physiological components. A typical breakdown for a normal-weight woman gaining 12 to 13 kilograms includes approximately 3.0 to 3.5 kilograms for the baby itself at full term, 0.6 to 0.9 kilograms for the placenta, 0.8 kilograms for amniotic fluid, 0.9 to 1.4 kilograms for uterine enlargement, 0.4 to 1.4 kilograms for breast tissue growth, 1.5 kilograms for increased blood volume, 1.0 to 1.5 kilograms from increased fluid retention in body tissues, and 2 to 4 kilograms of maternal fat stores needed to support breastfeeding. This breakdown explains why even women who gain within the recommended range typically retain several kilograms above their pre-pregnancy weight immediately after delivery, and why most of this additional weight resolves within six to twelve months postpartum when combined with breastfeeding and gradual return to activity.

Use our free Pregnancy Weight Gain Calculator to generate your personalised week-by-week weight gain chart, understand your recommended total gain range, and track your progress throughout your pregnancy. Always share your results with your midwife, obstetrician, or other healthcare provider, as individual circumstances may affect what is appropriate for your specific pregnancy.