This pregnancy weight gain calculator shows how much weight is recommended for your pre-pregnancy BMI and whether your gain so far is on track for your week of pregnancy. It follows the Institute of Medicine (IOM) guidelines, which are endorsed by the American College of Obstetricians and Gynecologists (ACOG), and covers twin pregnancies too.
Recommended weight gain by BMI
| Pre-pregnancy BMI | Total gain (one baby) | Weekly gain, 2nd and 3rd trimesters | Total gain (twins) |
|---|---|---|---|
| Under 18.5 (underweight) | 28–40 lb (12.5–18 kg) | 1–1.3 lb (0.45–0.59 kg) | No guideline |
| 18.5–24.9 (normal) | 25–35 lb (11.5–16 kg) | 0.8–1 lb (0.36–0.45 kg) | 37–54 lb (16.8–24.5 kg) |
| 25–29.9 (overweight) | 15–25 lb (7–11.5 kg) | 0.5–0.7 lb (0.23–0.32 kg) | 31–50 lb (14.1–22.7 kg) |
| 30 or more (obese) | 11–20 lb (5–9 kg) | 0.4–0.6 lb (0.18–0.27 kg) | 25–42 lb (11.3–19.1 kg) |
The guidelines assume a gain of 1.1–4.4 lb (0.5–2 kg) during the first trimester.
How the calculator works
It first works out your BMI from your height and pre-pregnancy weight. During the first 13 weeks, the suggested range rises steadily to 1.1–4.4 lb. After that, it follows a straight path to the full-term range for your BMI at 40 weeks, then compares it with what you have gained so far.
Worked example
A woman who is 5 ft 5 in (65 inches) tall and weighed 140 lb before pregnancy has a BMI of 23.3, in the normal range, so the recommended total is 25–35 lb. At week 20, the suggested gain so far is about 7.3–12.3 lb. Weighing 150 lb now, a 10 lb gain, she is within range.
Where the weight goes
At full term, only part of the gain is the baby. The rest is the placenta, amniotic fluid, larger uterus and breasts, extra blood and fluid, and fat stores that support breastfeeding.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy: 28–40 lb if underweight, 25–35 lb if normal weight, 15–25 lb if overweight and 11–20 lb if obese, for a single baby.
How much weight should I gain in the first trimester?
The guidelines assume about 1.1–4.4 lb (0.5–2 kg) in total for the first trimester. Many women gain little or even lose weight early on because of nausea.
What if I am gaining too much or too little?
Talk to your doctor or midwife. Gaining well outside the range is linked with a higher chance of some complications, but your care team will consider your full picture before suggesting changes.
Should I diet during pregnancy?
Weight-loss diets are not recommended during pregnancy unless your doctor advises it. Focus on nutritious food and appropriate activity instead.
Are the guidelines different for twins?
Yes. With twins the recommended totals are higher: 37–54 lb for normal weight, 31–50 lb for overweight and 25–42 lb for obese. There is no IOM range for underweight women carrying twins.
Related calculators
Sources
- MSD Manual: Guidelines for weight gain during pregnancy (IOM/ACOG)
- Institute of Medicine: Weight Gain During Pregnancy, Reexamining the Guidelines (2009)
Last reviewed: October 2026. This calculator is for information only and does not replace advice from a doctor or other qualified health professional.