How much weight you should gain in pregnancy depends on your body mass index (BMI) before pregnancy. Guidelines from the US Institute of Medicine, used by ACOG, recommend 11.5 to 16 kg (25 to 35 lb) for a BMI in the healthy range, more if you start underweight and less if you start with overweight or obesity. Most of the gain comes after week 20.
Recommended weight gain by BMI
| Pre-pregnancy BMI | Total gain | Weekly gain, 2nd and 3rd trimester |
|---|---|---|
| Under 18.5 | 12.5–18 kg (28–40 lb) | 0.44–0.58 kg (1–1.3 lb) |
| 18.5–24.9 | 11.5–16 kg (25–35 lb) | 0.35–0.50 kg (0.8–1 lb) |
| 25–29.9 | 7–11.5 kg (15–25 lb) | 0.23–0.33 kg (0.5–0.7 lb) |
| 30 or more | 5–9 kg (11–20 lb) | 0.17–0.27 kg (0.4–0.6 lb) |
In the first trimester, the usual gain is small: about 0.5 to 2 kg (1 to 4.4 lb) in total. Some people gain nothing or lose a little because of nausea.
How to use a pregnancy weight gain calculator
Our pregnancy weight gain calculator asks for your height and your weight before pregnancy. It works out your BMI and shows the total gain range that matches it.
Use your weight from just before pregnancy, not your current weight, or the result will be off. To see which week you are in, the due date calculator helps.
Twins
For twins, the guidelines suggest a higher total gain: 17 to 25 kg (37 to 54 lb) with a healthy BMI, 14 to 23 kg (31 to 50 lb) with overweight and 11 to 19 kg (25 to 42 lb) with obesity. There is not enough data to give a range for people who start underweight, so ask your care team.
Where the weight goes
The extra weight is not only the baby. It includes:
- The baby, the placenta and the amniotic fluid.
- A larger womb and larger breasts.
- More blood and other body fluids.
- Fat stores that your body builds to make breast milk.
Gaining more or less than expected
Gaining too much weight can raise the risk of gestational diabetes and high blood pressure, including pre-eclampsia. Gaining too little can be linked to premature birth and a low birth weight. Pregnancy is not the time to diet: if your gain is outside the range, talk to your midwife or doctor before changing what you eat.
Contact your midwife or maternity unit straight away if you notice sudden swelling of your face, hands or feet, especially with a headache or vision problems. These can be signs of pre-eclampsia.
How to track your weight
- Weigh yourself on the same scale, at the same time of day, no more than once a week.
- Compare the trend over several weeks, not single readings.
- Bring your notes to antenatal appointments.
About Bloom Private
Our calculators run in your browser and need no account. Bloom Private is an iPhone app for cycle tracking, useful before pregnancy and once your cycles return; it does not have a pregnancy mode. It is a tracking tool, not a medical device. Always follow the advice of your midwife or doctor.
Frequently Asked Questions
It depends on your BMI before pregnancy: 12.5–18 kg (28–40 lb) if underweight, 11.5–16 kg (25–35 lb) with a healthy BMI, 7–11.5 kg (15–25 lb) with overweight and 5–9 kg (11–20 lb) with obesity.
Usually about 0.5 to 2 kg (1 to 4.4 lb) in total. Most of the gain comes after week 20, and some people lose a little early on because of nausea.
It gives the recommended range for your pre-pregnancy BMI, based on Institute of Medicine guidelines. It cannot judge your individual situation, so discuss your gain with your midwife or doctor.