Pregnancy weight gain calculator
Enter your height, your weight before pregnancy and how many weeks pregnant you are. The calculator finds your pre-pregnancy BMI and shows the weight gain the Institute of Medicine (IOM) guidelines recommend, in total and by this week.
Your range
Enter your height and your weight before pregnancy to see your range.
How to use it
- Choose metric or US units and enter your height and your weight just before you got pregnant.
- Add how many weeks pregnant you are to see the range for this week. If you don't know, our due date calculator works it out.
- Add your weight now to see whether your gain so far is below, within or above that range.
- Tick twins if you are expecting two babies: the guidelines then give a total range only.
Recommended weight gain by BMI
| BMI before pregnancy | One baby | Twins |
|---|---|---|
| Underweight (below 18.5) | 28–40 lb (12.5–18 kg) | 50–62 lb (22.7–28.1 kg)* |
| Normal weight (18.5–24.9) | 25–35 lb (11.5–16 kg) | 37–54 lb (16.8–24.5 kg) |
| Overweight (25.0–29.9) | 15–25 lb (7–11.5 kg) | 31–50 lb (14.1–22.7 kg) |
| Obesity (30.0 or more) | 11–20 lb (5–9 kg) | 25–42 lb (11.3–19.1 kg) |
One baby: Institute of Medicine (IOM, 2009). Twins: as the CDC lists them, the IOM's provisional guidelines; *for underweight women with twins the IOM gave none, and the CDC's figure comes from a 2003 study by Luke and colleagues.
Recommended total gain by week (one baby)
| Week | underweight | normal weight | overweight | obesity |
|---|---|---|---|---|
| 12 | 1.0–4.1 lb | 1.0–4.1 lb | 1.0–4.1 lb | 1.0–4.1 lb |
| 16 | 4.1–8.4 lb | 3.8–7.8 lb | 2.6–6.7 lb | 2.2–6.1 lb |
| 20 | 8.1–13.6 lb | 7.3–12.3 lb | 4.7–9.7 lb | 3.7–8.4 lb |
| 24 | 12.1–18.9 lb | 10.8–16.9 lb | 6.8–12.8 lb | 5.1–10.8 lb |
| 28 | 16.0–24.2 lb | 14.4–21.4 lb | 8.8–15.8 lb | 6.6–13.1 lb |
| 32 | 20.0–29.5 lb | 17.9–25.9 lb | 10.9–18.9 lb | 8.1–15.4 lb |
| 36 | 24.0–34.7 lb | 21.5–30.5 lb | 12.9–21.9 lb | 9.5–17.7 lb |
| 40 | 28.0–40.0 lb | 25.0–35.0 lb | 15.0–25.0 lb | 11.0–20.0 lb |
We spread each IOM total range evenly over weeks 14 to 40, after the 0.5–2 kg (1.1–4.4 lb) first-trimester gain the IOM assumes, so week 40 matches the total. Real gain is rarely this even.
How fast should the weight go on?
After the first trimester the IOM suggests about 0.44–0.58 kg (1–1.3 lb) a week if you were underweight, 0.35–0.50 kg (0.8–1 lb) at a normal weight, 0.23–0.33 kg (0.5–0.7 lb) if overweight and 0.17–0.27 kg (0.4–0.6 lb) with obesity. In the first trimester its calculations assume only 0.5–2 kg (1.1–4.4 lb) in total.
Why the guidelines matter
The IOM committee set its ranges by looking at outcomes such as weight kept on after the birth, unplanned caesarean delivery and babies born small or large for their gestational age. Women who gained within the earlier guidelines had better pregnancy outcomes, although that evidence comes from observational studies. The CDC notes that only about 1 in 3 women gain within the recommended range; about 1 in 2 gain more.
What a calculator can't tell you
The IOM wrote these guidelines for women in the United States and says they may apply to other developed countries. They are meant to be used with good clinical judgment and a conversation with your care provider. They don't cover triplets or more, and the IOM notes that younger teenagers often need to gain more. If you have a medical condition, or your gain is well outside the range, ask your midwife or doctor.
These ranges are guidelines for planning; your midwife or doctor may advise a different goal.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. The IOM recommends 12.5–18 kg (28–40 lb) if you were underweight, 11.5–16 kg (25–35 lb) at a normal weight, 7–11.5 kg (15–25 lb) if overweight and 5–9 kg (11–20 lb) with obesity.
How much weight should I have gained by 20 weeks?
At a normal pre-pregnancy weight, about 3.4–5.6 kg (7.3–12.3 lb) by week 20, if the IOM total range is spread evenly after the first trimester. The calculator works it out for your own BMI and week.
How much weight should I gain in the first trimester?
Not much. The IOM's calculations assume 0.5–2 kg (1.1–4.4 lb) over the first trimester, and the CDC says you generally don't need extra calories then.
How much weight should I gain with twins?
The IOM's provisional guidelines are 16.8–24.5 kg (37–54 lb) at a normal weight, 14.1–22.7 kg (31–50 lb) if overweight and 11.3–19.1 kg (25–42 lb) with obesity. For underweight women the CDC lists 22.7–28.1 kg (50–62 lb), from a 2003 study.
How many extra calories do I need?
The CDC suggests about 340 extra calories a day in the second trimester and about 450 in the third, and generally none in the first.
What if I'm gaining more or less than the range?
Talk to your midwife or doctor. The IOM linked gains outside its ranges to outcomes such as weight kept on after the birth and babies born small or large for their age, but your provider can see the whole picture.
Sources
Also try: Pregnancy due date calculator