Pregnancy Weight Gain Calculator

Choose units. US mode takes pounds and inches; metric mode takes kilograms and centimetres. The ranges and the gain-so-far figure are always shown in pounds, because that is how the IOM table is published. To convert, 25-35 lb is about 11.5-16 kg.

Enter your pre-pregnancy weight and height. Use your weight just before you conceived. If you do not know it, the weight recorded at your first prenatal visit is the usual stand-in. For this example, 140 lb and 65 inches produce a BMI of 23.3, which the tool labels Normal weight. The metric default of 64 kg at 165 cm gives a BMI of 23.5 and lands in the same category.

Enter weeks pregnant. The field accepts 0 to 42. At 20 weeks, the results panel shows a total recommended gain of 25-35 lb, a second- and third-trimester rate of about 1 lb a week (0.8-1), and an expected gain by week 20 of about 10 lb.

Compare it with your own chart. That 10 lb is the average path through the guideline, made of 3 lb for the first 13 weeks plus 7 weeks at 1 lb a week. It is not a checkpoint you pass or fail. What matters is the pattern your provider sees across visits, and whether you are on course for the 25-35 lb total by delivery.

Pre-pregnancy BMI = 703 × weight (lb) ÷ height (in)², or weight (kg) ÷ height (m)² in metric mode.

Category lookup follows IOM Table S-1 in *Weight Gain During Pregnancy: Reexamining the Guidelines* (2009): BMI below 18.5 is underweight; 18.5 up to 25 is normal weight; 25 up to 30 is overweight; 30 and above is obese.

Total gain and weekly rate come straight from that table. Underweight: 28-40 lb total, mean 1 lb a week (range 1-1.3). Normal weight: 25-35 lb, mean 1 (0.8-1). Overweight: 15-25 lb, mean 0.6 (0.5-0.7). Obese: 11-20 lb, mean 0.5 (0.4-0.6).

Expected gain so far. For weeks 0-13 it is 3 lb × week ÷ 13, a straight line to 3 lb at the end of the first trimester. From week 14 on it is 3 lb + (week − 13) × the category's mean weekly rate. The week is capped at 42.

The 3 lb first-trimester figure is a midpoint. The IOM's weekly rates assume a first-trimester gain of roughly 1.1-4.4 lb (0.5-2 kg), and the tool picks one value inside that span so it can draw a single average path. It uses only the mean rate, so the gain-so-far number has no range around it, even though the weekly rate does.

Take 200 lb before pregnancy at 5 ft 4 in. BMI is 34.3, the obese category, so the total range narrows to 11-20 lb and the weekly pace drops to about 0.5 lb (0.4-0.6). At week 30 the expected gain is about 11.5 lb: 3 lb for the first trimester plus 17 weeks at 0.5 lb.

That figure already sits at the bottom of the 11-20 lb total, and it is expected to. The same path reaches 16.5 lb at week 40, inside the range. For comparison, the normal-weight example above would be at 20 lb by week 30 and 30 lb by week 40, which also lands inside its 25-35 lb range. The categories differ mainly in the slope after week 13, not in the first trimester.

Category edges are sharp. At 5 ft 5 in, 180 lb gives a BMI of 29.95, which is overweight, with a 15-25 lb range and 13.2 lb expected by week 30. At 182 lb the BMI is 30.3, which is obese, with an 11-20 lb range and 11.5 lb by week 30. Two pounds of starting weight move the guideline by several pounds. If your BMI sits right at a boundary, your provider may reasonably use judgment rather than the label.

The IOM ranges come from studies linking gain to outcomes such as baby's birth weight, preterm birth, caesarean delivery and weight kept after delivery. They describe what is associated with good outcomes across many pregnancies. They do not tell any one person what to weigh on a given Tuesday. The American College of Obstetricians and Gynecologists adopted these same IOM ranges in Committee Opinion 548 (2013), so your prenatal team is very likely using the same numbers.

If you are gaining faster than the path, do not start a diet, skip meals or cut food groups to get back inside the line. Pregnancy needs steady nutrition, and any change in eating or activity should come from your provider, who may suggest a dietitian. If you are gaining slowly, nausea, vomiting or food aversions are common reasons early on. Mention them, especially if you are losing weight or cannot keep food down.

Gain is also rarely a smooth line. It can stall for a few weeks and then jump, and fluid shifts alone can move the scale. One reading that is above or below the path is a question to raise at your next visit, not an emergency. Sudden swelling of the face or hands, or rapid gain over a few days, is different. Call your provider promptly about those.

The calculator applies the singleton table only. The same IOM report gives separate provisional ranges for twin pregnancies: 37-54 lb for normal weight, 31-50 lb for overweight and 25-42 lb for obese. It did not set a twin range for underweight women because there was not enough data. If you are carrying twins, the figures this tool shows will be too low for you. Use your provider's twin-specific plan instead.

There are no IOM ranges for triplets or more. Individual targets are also common when a pregnancy involves gestational or pre-existing diabetes, high blood pressure, a history of an eating disorder, or bariatric surgery before pregnancy. In all of these cases, your care team's plan takes priority over a general table.

This is an educational guide to the IOM table, not medical advice, and it cannot tell you whether your pregnancy is going well. It uses BMI, which reflects weight for height and not body composition. It assumes a single fetus. It draws one average path using a fixed 3 lb first-trimester gain and the mean weekly rate, with no range around the gain-so-far figure. It does not ask for your current weight, so it does not compare your actual gain with anything. It also does not account for medical conditions that lead providers to set individual targets. Anyone with a high-risk pregnancy, multiples, or concerns about eating should rely on their own clinician.

Weight-gain guidance is always read against how far along you are, so start with an accurate week count. The pregnancy calculator lays out the whole timeline and trimester milestones, the due date calculator estimates delivery from your last period, and the gestational age calculator gives an exact week-and-day figure to put in the weeks field here. To check the pre-pregnancy BMI category on its own, or to look at weight for height again after the baby arrives, the BMI calculator uses the same 18.5, 25 and 30 cut-offs.