Pregnancy Weight Gain Calculator
Enter your weight before pregnancy, your height and how many weeks pregnant you are. The calculator shows the weight gain range in the US national guidelines, at term and at your current week, for one baby or twins.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
Units
Pregnancy
Counted from the first day of your last period.
Enter your weight before pregnancy, your height and your current week to see the guideline range.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
The calculator works out your pre-pregnancy body mass index (BMI): weight in kilograms divided by height in metres squared. It then looks up the total gain for that BMI group in the 2009 Institute of Medicine guidelines. For one baby: BMI under 18.5, 12.5 to 18 kg (28 to 40 lb); BMI 18.5 to 24.9, 11.5 to 16 kg (25 to 35 lb); BMI 25 to 29.9, 7 to 11.5 kg (15 to 25 lb); BMI 30 or more, 5 to 9 kg (11 to 20 lb).
For the range at your current week, it follows the same guidelines. They assume a gain of 0.5 to 2 kg (1.1 to 4.4 lb) across the first 13 weeks, then a steady gain each week up to the total at 40 weeks. So the range at week 26 is the week 13 range plus 13/27 of the rest. The guideline weekly rates for one baby after week 13 are about 0.5 kg for a BMI under 18.5, 0.4 kg for 18.5 to 24.9, 0.3 kg for 25 to 29.9 and 0.2 kg for 30 or more.
For twins the guidelines give provisional totals at term only: BMI 18.5 to 24.9, 17 to 25 kg (37 to 54 lb); BMI 25 to 29.9, 14 to 23 kg (31 to 50 lb); BMI 30 or more, 11 to 19 kg (25 to 42 lb). They give no twin figure for a BMI under 18.5. For that group the calculator shows the 50 to 62 lb listed by the CDC, which comes from a single 2003 study. There is no week-by-week range for twins.
What it cannot tell you
- The ranges describe groups of women, not you. Many healthy pregnancies end with a gain above or below the range, and weight gain is rarely steady from week to week. Your midwife or doctor's advice comes first.
- BMI uses only height and weight. It does not account for muscle, body shape, age or ethnic background, and the guidelines are based mostly on US data. Other countries, including the UK, do not set formal targets.
- It does not cover triplets or more, and the twin ranges are provisional.
- Contact your midwife or doctor if you are losing weight, cannot keep food or drink down, or gain weight very suddenly together with swelling, a bad headache or changes in your sight. If thinking about weight or food is causing you distress, tell them. You can ask not to be told your weight at appointments.
Apps that do this for you
A calculator answers once. These apps keep track over time. Compare all pregnancy and parenting apps.
Baby Connect
A baby tracker: log sleep, feeds and diapers and share it with every caregiver, on phone, web and Apple Watch.
Baby Daybook
A baby tracker: feeds, sleep, nappies and growth, with sleep predictions and family sync
BabyCenter
A pregnancy and baby tracker: week-by-week updates, handy tools, articles and a parent community.
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Common questions
The US guidelines suggest a total pregnancy weight gain of 11.5 to 16 kg (25 to 35 lb) for one baby if your pre-pregnancy BMI was 18.5 to 24.9. The range is 12.5 to 18 kg for a BMI under 18.5, 7 to 11.5 kg for a BMI of 25 to 29.9 and 5 to 9 kg for a BMI of 30 or more. These are guides, and many healthy pregnancies fall outside them.
Weight gain in the first trimester is usually small. The US guidelines assume 0.5 to 2 kg (1.1 to 4.4 lb) in total over the first 13 weeks. Some women gain nothing or lose a little because of nausea, which is common. Tell your midwife or doctor if you cannot keep food or drink down.
After the first trimester, the guideline weight gain for one baby is about 0.4 kg (roughly 1 lb) a week if your pre-pregnancy BMI was 18.5 to 24.9. It is about 0.5 kg a week for a BMI under 18.5, 0.3 kg for a BMI of 25 to 29.9 and 0.2 kg for a BMI of 30 or more. Real weight gain goes up and down from week to week.
For a twin pregnancy the US guidelines suggest a total gain of 17 to 25 kg (37 to 54 lb) if your pre-pregnancy BMI was 18.5 to 24.9. The range is 14 to 23 kg for a BMI of 25 to 29.9 and 11 to 19 kg for a BMI of 30 or more. These twin ranges are provisional because less research is available.
Pregnancy weight gain is much more than the baby. It also includes the placenta, the fluid around the baby, a larger womb and breasts, extra blood and body fluid, and some stored fat for breastfeeding. The baby is usually only about a quarter to a third of the total gain.