Pregnancy Weight Gain Calculator
Enter your weight from before pregnancy in pounds or kilograms and your height in feet and inches or centimeters. The calculator shows how much weight the Institute of Medicine (IOM, now the National Academy of Medicine) recommends gaining for your BMI. Tick Twin pregnancy for the IOM's twin ranges. For a single baby you can also enter the current week and your gain so far, and the calculator checks that gain against a range for that week. The IOM gives weekly rates only for the second and third trimesters, which the calculator starts at week 14. For weeks 1 to 13 the IOM gives one total for the whole first trimester, 1.1–4.4 lb (0.5–2 kg), so the range for those weeks is the calculator's own straight-line estimate of that total, not an IOM figure for the week.
Current Progress (optional)
How to use the Pregnancy Weight Gain Calculator
- Enter your numbers in the Pregnancy Weight Gain Calculator above.
- Press the Calculate button to see the result.
- To try other numbers, change any value and press the button again.
IOM weight gain guidelines (2009)
Underweight (BMI under 18.5): 28–40 lb in total, 1–1.3 lb a week · · · Normal (18.5–24.9): 25–35 lb, 0.8–1 lb a week · · · Overweight (25–29.9): 15–25 lb, 0.5–0.7 lb a week · · · Obese (30+): 11–20 lb, 0.4–0.6 lb a week
The calculator rounds your pre-pregnancy BMI to 2 decimals and picks the total range from it. The weekly rates are the IOM's ranges for the 2nd and 3rd trimesters, which assume a gain of 1.1–4.4 lb in the first trimester. That 1.1–4.4 lb is a total for the whole trimester, not a weekly pace. Pregnancy weeks count from your last period and conception comes about two weeks later, so the week check's low end is 0 lb at week 2 and climbs 0.1 lb a week to 1.1 lb at week 13. The high end stays at 4.4 lb until then. Week 6, for example, is checked against 0.4–4.4 lb. After week 13 the check adds the low weekly rate to 1.1 lb and the high one to 4.4 lb for each week past 13. The IOM's weekly rates add up to a little less than its totals, so at a normal BMI week 40 is checked against 22.7–31.4 lb while the recommended total is 25–35 lb. In metric mode the calculator converts each of these pound figures to kilograms at 1 lb = 0.45359237 kg and shows the result in kg. The IOM also prints its own rounded kilogram figures, so the converted ones can differ from them slightly.
Worked example
A woman who was 5'5" and 140 lb before pregnancy has a BMI of 23.3, normal weight, so her recommended total is 25–35 lb. At week 20 the calculator expects 6.7–11.4 lb so far. The low end is 1.1 + 0.8 × 7 and the high end is 4.4 + 1 × 7, for the 7 weeks after week 13. Entered in metric as 165.1 cm and 63.5 kg, she gets the same BMI of 23.3, and week 20 reads 3.04–5.17 kg.
Frequently asked questions
What happens if I gain too much?
Excessive gain raises risks of gestational diabetes, hypertension, larger-than-average babies, complicated delivery and more difficulty losing weight postpartum.
What if I'm carrying twins?
Tick Twin pregnancy. The calculator then shows the IOM's provisional twin totals, which are 37–54 lb at a normal BMI, 31–50 lb when overweight and 25–42 lb when obese. Metric shows them converted to kilograms. The IOM gives no twin range for an underweight BMI, so the calculator shows none and suggests asking your midwife or doctor. The IOM gives no weekly rate for twins either, so the week check works for a single baby only. There is no setting for triplets.
Does it work in kilograms?
Yes. Pick Metric and enter your weight and your gain so far in kilograms and your height in centimeters. The recommended total, the weekly rates and the week check then show in kilograms, converted from the IOM's pound figures. Each unit keeps its own gain entry, so switching units never reads pounds as kilograms.