Pregnancy Weight Gain Calculator: IOM Guidelines by Week
See how much weight to gain in pregnancy by the IOM 2009 guidelines, from your pre-pregnancy BMI, for one baby or twins, with the range for your current week and your gain so far. Metric or US units. Nothing is uploaded.
Enter your height, pre-pregnancy weight and week to see your range.
About the Pregnancy Weight Gain Calculator
The Pregnancy Weight Gain Calculator shows how much weight is recommended during pregnancy, following the 2009 guidelines of the Institute of Medicine (IOM), now the National Academy of Medicine. You enter your height and your weight before pregnancy, the current week of pregnancy, and whether you are expecting one baby or twins. The calculator works out your pre-pregnancy body mass index (BMI), the total gain recommended for your BMI category, and the gain expected by the week you entered. Add your current weight to see how your gain so far compares with that week's range.
Heights can be entered in centimetres or in feet and inches, and weights in kilograms or pounds. Every range is shown in both units.
This is an estimate, not medical advice. Healthy pregnancies vary, and your midwife or doctor may set a different target for you, for example if you have diabetes or are carrying more than two babies.
How to use it
Steps
- Choose One baby or Twins.
- Choose metric or US customary units and enter your height.
- Enter your weight before pregnancy and the current week, from 1 to 42.
- Optionally enter your current weight.
- Read the total recommended gain, the range for your week and, if you entered it, your gain so far.
The IOM 2009 ranges
Your BMI before pregnancy sets the range: underweight below 18.5, normal 18.5 to 24.9, overweight 25 to 29.9 and obese 30 or more.
Total gain
- Underweight: 12.5–18 kg (28–40 lb) for one baby; no guideline for twins.
- Normal: 11.5–16 kg (25–35 lb) for one baby; 17–25 kg (37–54 lb) for twins.
- Overweight: 7–11.5 kg (15–25 lb) for one baby; 14–23 kg (31–50 lb) for twins.
- Obese: 5–9 kg (11–20 lb) for one baby; 11–19 kg (25–42 lb) for twins.
Per week from week 14
- Underweight: 0.44–0.58 kg (about 1–1.3 lb) a week.
- Normal: 0.35–0.50 kg (about 0.8–1 lb) a week.
- Overweight: 0.23–0.33 kg (about 0.5–0.7 lb) a week.
- Obese: 0.17–0.27 kg (about 0.4–0.6 lb) a week.
The twin ranges are provisional, and the IOM did not set a range for twins when the pre-pregnancy BMI is underweight, so the calculator says so instead of guessing.
The range for your week
The guidelines assume a gain of 0.5 to 2 kg over the first trimester, weeks 1 to 13. The calculator spreads that evenly over those weeks. From week 14 it adds the weekly rate for your BMI category for every week after week 13:
Worked example
At 165 cm and 60 kg before pregnancy, BMI is 60 ÷ 1.65² = 22.0, which is normal. At week 20 the expected gain is 0.5 + 7 × 0.35 = 2.95 kg to 2 + 7 × 0.50 = 5.5 kg. A current weight of 64 kg means a gain of 4 kg, within that range. The total for the whole pregnancy is 11.5 to 16 kg.
The IOM gives no weekly rates for twins, so for twins the calculator shows the total range only.
Privacy
Nothing is uploaded. Every calculation runs in your browser, and your measurements never leave your device.
Related tools
Find your due date and how far along you are with the Due Date Calculator or the Pregnancy Calculator. Check your BMI before pregnancy with the BMI Calculator, and convert kilograms and pounds with the Mass Converter.
Sources
- Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. The National Academies Press, 2009. Table S-1 and the provisional twin guidelines.
- Centers for Disease Control and Prevention. Weight gain during pregnancy.
Open-source credits
The calculations are implemented in-house in TypeScript, with no third-party library. They follow the IOM 2009 weight gain guidelines and the WHO adult BMI categories.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. The IOM 2009 guidelines recommend 12.5 to 18 kg if you were underweight, 11.5 to 16 kg at a normal BMI, 7 to 11.5 kg if overweight and 5 to 9 kg if obese, for one baby. Your midwife or doctor may suggest a different target.
How much weight should I gain with twins?
The IOM's provisional ranges for twins are 17 to 25 kg at a normal BMI, 14 to 23 kg if overweight and 11 to 19 kg if obese. There is no IOM range for twins when the pre-pregnancy BMI is underweight, and no weekly rates for twins.
How is the range for my week worked out?
The guidelines assume 0.5 to 2 kg over the first 13 weeks, which the calculator spreads evenly across those weeks. From week 14 it adds the IOM weekly rate for your BMI category, for example 0.35 to 0.50 kg a week at a normal BMI.
Which weight should I enter as my pre-pregnancy weight?
Use your weight just before you became pregnant, or the weight measured at your first antenatal appointment if you are not sure. The BMI category it gives sets every range on the page.
Is my information stored or sent anywhere?
No. Everything is calculated in your browser. Your measurements are never sent anywhere and are gone when you close the page.