This calculator gives general estimates for information only. It does not replace advice from your doctor, pharmacist or another qualified health professional.
How much weight to gain
Gaining enough weight during pregnancy supports the baby’s growth, but gaining too much raises the risk of gestational diabetes, high blood pressure, cesarean delivery and weight that stays after birth. The recommended amount depends on your body mass index (BMI) before pregnancy: the lower it was, the more you are advised to gain. The ranges below come from the 2009 Institute of Medicine (IOM) guidelines, endorsed by the American College of Obstetricians and Gynecologists, for a single baby.
Recommended total gain
| Pre-pregnancy BMI | Category | Total gain | Weekly gain, 2nd and 3rd trimesters |
|---|---|---|---|
| Below 18.5 | Underweight | 28–40 lb | about 1 lb (1–1.3) |
| 18.5–24.9 | Healthy weight | 25–35 lb | about 1 lb (0.8–1) |
| 25–29.9 | Overweight | 15–25 lb | about 0.6 lb (0.5–0.7) |
| 30 or more | Obesity | 11–20 lb | about 0.5 lb (0.4–0.6) |
In the first trimester, a gain of 1.1 to 4.4 lb is typical, and some women gain nothing because of nausea.
How the weekly range is calculated
The calculator spreads 1.1 to 4.4 lb evenly over weeks 1 to 13, then spreads the rest of the total range evenly from week 14 to week 40. Weeks are counted from the first day of your last period, as your doctor does.
Worked example: 150 lb, 5 ft 6 in, week 20
- BMI: 150 lb at 66 in gives 24.2, a healthy weight.
- Total gain: 25 to 35 lb by week 40.
- At week 20: 1.1 + 7 ÷ 27 × (25 − 1.1) = 7.3 lb to 4.4 + 7 ÷ 27 × (35 − 4.4) = 12.3 lb.
- Weighing 160 lb now, a gain of 10 lb, is within the range.
Range by week (healthy pre-pregnancy BMI)
| Week | Gain so far |
|---|---|
| 8 | 0.7–2.7 lb |
| 13 | 1.1–4.4 lb |
| 20 | 7.3–12.3 lb |
| 26 | 12.6–19.1 lb |
| 30 | 16.2–23.7 lb |
| 36 | 21.5–30.5 lb |
| 40 | 25–35 lb |
Where the weight goes
At term, a typical 30 lb gain is roughly: baby 7.5 lb, placenta 1.5 lb, amniotic fluid 2 lb, larger uterus 2 lb, breasts 2 lb, extra blood 4 lb, other fluids 4 lb, and fat stores 7 lb that help with breastfeeding.
Good to know
- Twins: the IOM suggests 37 to 54 lb for a healthy BMI, 31 to 50 lb if overweight and 25 to 42 lb with obesity.
- Trend over numbers: weekly gain varies with water retention; look at the curve over several weeks.
- Eating for two is a myth: the extra need is about 340 calories a day in the second trimester and 450 in the third, and none in the first.
- A sudden gain of several pounds in a few days, with swelling of the face or hands, needs a prompt call to your doctor.