How much weight should I gain during pregnancy?
Gaining the right amount of weight in pregnancy supports your baby’s growth and your own health. The amount depends mainly on your body mass index (BMI) before pregnancy. Women who start pregnancy underweight need to gain more; women who start overweight or with obesity need to gain less. This pregnancy weight gain calculator uses the guidelines from the U.S. Institute of Medicine (IOM, now the National Academy of Medicine), which are used by doctors worldwide.
How the calculator works
- It calculates your pre-pregnancy BMI from your height and weight before pregnancy.
- It assigns your IOM group and total recommended gain.
- For your current week it estimates a healthy range: about 0.5–2 kg in the first trimester (weeks 1–13), then the recommended weekly rate for your group in the second and third trimesters.
Example: a woman with a pre-pregnancy BMI of 22 (healthy weight) at week 24 should have gained roughly 0.5 + 11 × 0.35 to 2 + 11 × 0.50 = 4.4–7.5 kg, heading for a total of 11.5–16 kg.
Pregnancy weight gain chart (IOM 2009)
| Pre-pregnancy BMI | Total gain (one baby) | Weekly gain, 2nd–3rd trimester | Total gain (twins) |
|---|---|---|---|
| Underweight (under 18.5) | 12.5 – 18 kg (28–40 lb) | 0.44 – 0.58 kg (1–1.3 lb) | No guideline |
| Healthy weight (18.5 – 24.9) | 11.5 – 16 kg (25–35 lb) | 0.35 – 0.50 kg (0.8–1 lb) | 17 – 25 kg (37–54 lb) |
| Overweight (25 – 29.9) | 7 – 11.5 kg (15–25 lb) | 0.23 – 0.33 kg (0.5–0.7 lb) | 14 – 23 kg (31–50 lb) |
| Obesity (30 and above) | 5 – 9 kg (11–20 lb) | 0.17 – 0.27 kg (0.4–0.6 lb) | 11 – 19 kg (25–42 lb) |
Where does pregnancy weight go?
At full term, a typical gain of about 12 kg is made up of the baby (3–3.5 kg), placenta (0.7 kg), amniotic fluid (0.8 kg), larger uterus and breasts (1.4 kg), extra blood and fluid (2.5–3 kg) and maternal fat stores for breastfeeding (3–4 kg).
Benefits of healthy pregnancy weight gain
- Healthy baby growth and lower risk of low birth weight or premature birth.
- Lower risk of gestational diabetes, high blood pressure and pre-eclampsia when gain is not excessive.
- Easier delivery and lower chance of caesarean section linked to a very large baby.
- Easier return to your pre-pregnancy weight after birth.
Health warnings
- Never diet to lose weight during pregnancy unless your obstetrician specifically advises it.
- Sudden weight gain, swelling of the face or hands, headaches or vision changes can be signs of pre-eclampsia — seek medical care urgently.
- Severe vomiting with weight loss (hyperemesis gravidarum) needs medical treatment.
- This calculator is for general information. Your doctor or midwife may set a different target for you.
- Teenage pregnancies and pregnancies with medical conditions need individual advice.
Eating well for a healthy pregnancy
You don’t need to “eat for two”. Extra energy needs are small: about 340 kcal a day in the second trimester and 450 kcal in the third — roughly a bowl of yoghurt with fruit and nuts, or an egg sandwich. Focus on protein, iron, folate, iodine, calcium, vitamin D and omega-3s. Read our trimester guides: first trimester, second trimester and third trimester, plus gestational diabetes.
Frequently asked questions
How much weight should I gain in the first trimester?
Most women gain only 0.5–2 kg (1–4.5 lb) in the first 13 weeks. Some lose a little because of nausea, which is usually fine if it is short-lived.
How much weight should I gain per week in pregnancy?
In the second and third trimesters, women with a healthy pre-pregnancy BMI should gain about 0.35–0.5 kg a week. Underweight women should gain a bit more, and overweight women less.
Is it okay to lose weight during pregnancy if I am overweight?
Weight loss is not usually recommended in pregnancy. Instead, aim for the lower gain range for your BMI group through healthy eating and activity, with guidance from your doctor.
How much weight should I gain with twins?
The IOM provisional guidelines for twins are 17–25 kg for healthy-weight women, 14–23 kg for overweight women and 11–19 kg for women with obesity.
How many extra calories do I need in pregnancy?
Usually none in the first trimester, about 340 kcal a day in the second and about 450 kcal a day in the third. Needs vary with activity and starting weight.
Sources
- Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. 2009.
- American College of Obstetricians and Gynecologists. Committee Opinion No. 548: Weight gain during pregnancy.
- WHO recommendations on antenatal care for a positive pregnancy experience. 2016.