Estimate a healthy weight range and a week-by-week weight-gain schedule during pregnancy, based on the Institute of Medicine (IOM) guidelines and your pre-pregnancy BMI.
The pregnancy weight gain calculator on this page estimates how much weight you should gain during pregnancy and shows a week-by-week target range from conception to delivery. Gaining the right amount of weight is one of the most important things you can do for a healthy pregnancy. Too little weight gain is linked to low birth weight and premature birth, while too much raises the risk of gestational diabetes, high blood pressure, a difficult delivery, and weight that is hard to lose afterward. This tool is based on the widely used guidelines from the Institute of Medicine (now the National Academy of Medicine), which tie recommended gain to your pre-pregnancy body mass index (BMI).
Enter your current pregnancy week, whether you are carrying twins, your height, your pre-pregnancy weight, and your current weight. The calculator returns your recommended weight range for this week, your target range at delivery, your pre-pregnancy BMI category, and a complete table showing the healthy weight and weight-gain range for every week of your pregnancy. It works in both US and metric units.
There is no single right number — the healthy amount depends on your weight before you became pregnant. A woman who was underweight needs to gain more than one who was already overweight. The Institute of Medicine guidelines set the following total recommended gains for a single baby:
For women carrying twins, the recommended gains are higher:
The calculator automatically determines your BMI category from the height and pre-pregnancy weight you enter, then applies the matching range. There are no separate official twin guidelines for underweight women, so the calculator uses the normal-weight twin range in that case.
Body mass index is a measure of body weight relative to height, calculated as weight in kilograms divided by height in meters squared. It is the starting point for every pregnancy weight-gain recommendation because it gives a simple, standardized way to gauge whether someone began pregnancy underweight, at a healthy weight, overweight, or obese. Because the guidelines hinge on the weight you were before conceiving, it is important to enter your true pre-pregnancy weight rather than your current weight. If you are not sure of your exact starting weight, use the best estimate you have — your most recent pre-pregnancy doctor's visit is a good reference.
Weight gain is not spread evenly. In the first trimester (weeks 1 to 13), most women gain very little — only about 1 to 4.4 pounds (0.5 to 2 kg) total — because the baby is still tiny and many women experience nausea that limits appetite. The bulk of healthy weight gain happens in the second and third trimesters, when the baby grows rapidly. During this period, a steady gain of roughly half a pound to one pound per week is typical for a woman of normal weight. The calculator models exactly this pattern: a gentle ramp during the first trimester followed by a steady weekly increase through delivery, producing the week-by-week range shown in the results table.
It is reassuring to understand that pregnancy weight is not simply fat. For a typical 30-pound (13.6 kg) gain, the weight is distributed roughly as follows:
The fat stores are an essential energy reserve for the demands of late pregnancy, labor, and breastfeeding, which is why some fat gain is both normal and healthy.
Staying within the recommended range matters because both extremes carry risks. Gaining too little can lead to a baby that is small for gestational age, increases the chance of preterm birth, and may signal that the baby is not getting enough nutrients. Gaining too much increases the likelihood of gestational diabetes, preeclampsia (pregnancy-related high blood pressure), a larger-than-average baby that complicates delivery, a higher chance of cesarean section, and greater difficulty returning to a healthy weight after birth. Excess gain also raises the long-term risk of obesity for both mother and child. The goal is steady, moderate gain within your personalized range — not a strict number, but a healthy band to aim for.
Some circumstances call for individualized guidance that goes beyond the standard ranges. Women carrying twins or higher-order multiples need substantially more weight gain, which this calculator accounts for with the twin option. Teenagers, women of short stature, and those with certain medical conditions such as diabetes or thyroid disorders may receive customized targets from their providers. Severe morning sickness (hyperemesis gravidarum) can cause weight loss in early pregnancy that needs medical attention. In all of these cases, treat the calculator's output as a general reference and defer to the personalized advice of your healthcare team.
Much of the weight gained during pregnancy comes off quickly: the baby, placenta, and amniotic fluid account for a significant portion at delivery, and fluid losses continue over the following weeks. The remaining fat stores typically take longer to lose. Breastfeeding can help, as it uses additional energy, and a gradual return to physical activity combined with healthy eating supports steady postpartum weight loss. Most experts advise patience — it took nine months to gain the weight, and a similar timeframe to lose it is reasonable and healthy. Crash dieting is discouraged, especially while breastfeeding.
The results include a complete week-by-week table covering all 40 weeks of pregnancy. For each week it shows two things: the recommended weight range (your pre-pregnancy weight plus the healthy gain for that point) and the recommended weight gain (the gain alone). The current week you selected is highlighted so you can find it at a glance. Reading down the table, you will notice the values barely move during the first trimester and then climb steadily from week 14 onward — the visual signature of healthy pregnancy weight gain. You can use the table to set a personal target for any upcoming week, to check whether last week's weigh-in was on track, or simply to understand the trajectory ahead. Because the entire schedule is derived from your own height, pre-pregnancy weight, and BMI category, it is personalized rather than a one-size-fits-all chart.
It can seem counterintuitive that the recommendation is anchored to the weight you were before becoming pregnant rather than your weight today. The reason is that the IOM guidelines are built around pre-pregnancy BMI, which best predicts healthy outcomes for both mother and baby. A woman who started underweight has fewer nutrient reserves and needs to gain more to support the pregnancy, while a woman who started with obesity already carries energy reserves and can safely gain less. Your current weight is still important — the calculator uses it to tell you whether you are presently within, below, or above the healthy band — but the size of that band is set by where you began. This is also why an accurate pre-pregnancy figure produces the most reliable guidance; if you only have an approximate number, the results are still useful but should be treated as an estimate.
The weight-gain ranges used here come from the Institute of Medicine, which first issued pregnancy weight recommendations in 1990 and updated them in 2009 to reflect rising rates of overweight and obesity and a growing body of research linking maternal weight to birth outcomes. The 2009 revision, developed with the National Research Council, defined the four BMI-based categories and added specific guidance for women carrying twins. These ranges are now the standard reference used by obstetricians, midwives, and public-health organizations across the United States and are echoed by bodies such as the American College of Obstetricians and Gynecologists. They represent a consensus of evidence rather than any single study, which is why they have remained stable and widely trusted. As with any population-level guideline, they describe a healthy range for most pregnancies, and individual circumstances can warrant adjustment under a provider's care.
Very little. Most women gain only about 1 to 4.4 pounds (0.5 to 2 kg) total during the entire first trimester, regardless of their pre-pregnancy BMI. Slow gain in these early weeks is completely normal, especially if nausea reduces your appetite. The faster, steady gain begins in the second trimester.
An occasional week outside the range is rarely a concern — weight fluctuates naturally. What matters is the overall trend. If you are consistently above or below your recommended range, talk to your healthcare provider, who can check for underlying causes and help you adjust your diet and activity. Do not attempt to diet to lose weight during pregnancy unless specifically directed by your provider.
Yes. Carrying twins requires significantly more weight gain — for example, 37 to 54 pounds for a woman of normal pre-pregnancy weight, compared with 25 to 35 pounds for a single baby. Select the twins option in the calculator to see the higher recommended range.
Enter both. The calculator uses your pre-pregnancy weight together with your height to determine your BMI category and recommended range, and it uses your current weight to tell you whether you are within, below, or above the range for your current week.
The ranges are based on the Institute of Medicine's evidence-based guidelines and are the same ones used by most healthcare providers in the United States. However, they are general recommendations for healthy pregnancies. Your provider may adjust them based on your individual health, so always use the calculator alongside professional medical advice.
Yes. Insufficient maternal weight gain is associated with lower birth weight and a higher chance of prematurity, while excessive gain is associated with larger babies and delivery complications. Staying within the recommended range gives your baby the best chance of a healthy birth weight.
This Pregnancy Weight Gain Calculator is provided for educational and general informational purposes only and is based on Institute of Medicine population guidelines. It is not medical advice and does not replace the personalized guidance of a qualified healthcare provider. Every pregnancy is different; always consult your obstetrician or midwife about your weight, diet, and overall health during pregnancy.