Pregnancy Weight Gain Calculator: How Much Should I Gain?
Enter your weight before pregnancy and your height to see your recommended total gain. Add your current week and weight to check whether you're on track.
Recommended total weight gain
- Per week in the 2nd and 3rd trimesters
- Gained so far
Recommended ranges
How much you should gain depends on your body mass index (BMI) before pregnancy. The calculator uses the 2009 Institute of Medicine (IOM) guidelines, which the American College of Obstetricians and Gynecologists (ACOG) also endorses.
| BMI before pregnancy | Total (one baby) | Per week, 2nd and 3rd trimesters | Twins |
|---|---|---|---|
| Underweight (under 18.5) | 28–40 lb | 1–1.3 lb | No recommendation |
| Healthy weight (18.5 to under 25) | 25–35 lb | 0.8–1 lb | 37–54 lb |
| Overweight (25 to under 30) | 15–25 lb | 0.5–0.7 lb | 31–50 lb |
| Obesity (30 or more) | 11–20 lb | 0.4–0.6 lb | 25–42 lb |
Prefer kilograms? Switch the calculator to kg / cm; the ranges are the same, converted from the original kilogram values.
When you enter your week, the calculator assumes a total of 1.1–4.4 lb in the first trimester and the weekly rates above after that, to show your recommended range for that week. Treat it as a guide: the trend over several weeks matters more than any single weigh-in.
Why it depends on your BMI
Part of pregnancy weight is the baby, placenta, amniotic fluid, extra blood volume and a growing uterus; part is fat stored for breastfeeding. If you start underweight, your body needs more of those stores; if you start overweight, more of them are already there. That’s why the recommended range narrows as BMI goes up.
Gaining much less than recommended is linked to a lower birth weight, and gaining much more is linked to a larger baby, a higher chance of a cesarean and weight that’s harder to lose afterwards. These are risks, not certainties; being a little outside the range usually isn’t a problem.
Why the UK doesn’t use target ranges
This is where guidelines really differ. In the US, the IOM ranges are widely used and weight is tracked at prenatal visits. The UK’s national guideline (NICE) doesn’t adopt the IOM ranges; it recommends measuring weight and height at the booking appointment and not routinely re-weighing afterwards unless there’s a specific reason. The focus is on healthy eating and staying active.
The “eating for two” myth
Your energy needs rise much less than most people think, and barely at all in early pregnancy. “Eating for two” is one of the most common reasons people gain more than recommended. Variety, vegetables and fruit, enough protein, and nutrients like iron and calcium matter far more than portion size. Weight-loss diets, on the other hand, aren’t recommended during pregnancy.
Frequently asked questions
How much weight should I gain during pregnancy?
It depends on your BMI before pregnancy. People who start underweight are advised to gain more, and those who start overweight or with obesity are advised to gain less. The calculator shows your range.
I haven't gained anything in the first trimester, or I've lost weight. Is that a problem?
Gaining little or losing a bit in the first trimester is common, often because of nausea. Most weight is gained in the second and third trimesters. If you can't keep fluids down, call your provider.
How much should I gain with twins?
More weight gain is recommended with twins. Tick "Twin pregnancy" in the calculator to see your total range.
Do I need to eat for two?
No. Your energy needs barely change in early pregnancy. The quality of what you eat matters far more than the quantity.
Should I try to lose weight while pregnant?
Weight-loss diets aren't recommended during pregnancy. If you started pregnancy overweight, the goal is to stay within your recommended range; plan that with your provider or a dietitian.
About this page
- Medical review
- Emergency medicine physician · October 24, 2026
- Last updated
Sources
- Weight Gain During Pregnancy: Reexamining the Guidelines. Institute of Medicine (IOM) and National Research Council, National Academies Press, 2009.
- Weight Gain During Pregnancy. Committee Opinion No. 548. American College of Obstetricians and Gynecologists (ACOG), 2013.
- Weight management before, during and after pregnancy. Public health guideline PH27. National Institute for Health and Care Excellence (NICE), 2010.
- Obesity: preventing and managing the global epidemic. WHO Technical Report Series 894. World Health Organization (WHO), 2000.
This page is for general information and does not replace an examination or diagnosis.