Pregnancy Weight Gain Calculator
Track recommended pregnancy weight gain based on your pre-pregnancy BMI using IOM guidelines, with week-by-week expected gain for singleton and twin pregnancies.
| BMI Category | Singleton Gain | Twins Gain |
|---|---|---|
| Enter your details to see guidelines | ||
* IOM 2009 guidelines. Weight gain is distributed: ~1–4.5 lbs in 1st trimester, then steady weekly gain in 2nd & 3rd trimesters.
Track how much weight gain is recommended during pregnancy based on your pre-pregnancy BMI, using Institute of Medicine (IOM) guidelines for both singleton and twin pregnancies.
How Pregnancy Weight Gain Calculator Works
Your pre-pregnancy BMI is calculated the standard way (weight ÷ height²) and sorted into one of four IOM categories — underweight, normal, overweight, or obese — each carrying a different recommended total gain range. Underweight women are advised to gain the most (28–40 lbs), while those in the obese category are advised to gain the least (11–20 lbs), reflecting different nutritional starting points. Twin pregnancies carry higher recommended ranges across every category.
Expected gain by your current week assumes roughly 2.2 lbs total gained gradually across the first trimester, followed by a steady weekly rate for the remainder of pregnancy — that weekly rate itself depends on your BMI category, running higher for underweight and normal-BMI women (about 1 lb/week) and lower for overweight and obese women (0.5–0.6 lb/week).
The "remaining to gain" figure compares your estimated gain-to-date against the midpoint of your recommended total range, giving a rough sense of whether your trajectory is tracking on pace — though actual week-to-week gain varies significantly between individuals and pregnancies.
See It In Action
Who Uses Pregnancy Weight Gain Calculator and Why
- Checking whether your weight gain so far is broadly in line with IOM guidelines for your pre-pregnancy BMI category.
- Getting a sense of the total recommended gain range early in pregnancy to set expectations.
- Comparing recommended ranges for a twin pregnancy against a singleton one.
Mistakes to Avoid
- Treating the weekly expected-gain figure as something to hit precisely — real week-to-week gain varies a lot between individuals and even between trimesters of the same pregnancy.
- Using a current (not pre-pregnancy) weight and height to calculate the BMI category the recommendation is based on, which skews which range you're compared against.
- Trying to actively restrict gain based on this tool's numbers rather than treating them as general guidelines discussed with a prenatal care provider.
Tips for Best Results
- Use your pre-pregnancy weight, not a current weight, when entering your BMI category input — the whole recommendation range is built around that starting point.
- Look at the total range for your BMI category rather than fixating on the single midpoint the "remaining to gain" figure compares against.
Fixing Common Problems
My gain-to-date looks like it's tracking above or below the estimate. — This is a rough comparison against a general weekly-rate assumption, not a personalized trajectory — pregnancy weight gain naturally varies, and your prenatal provider tracks your specific pattern over time far more reliably than a single calculator comparison.
Terms Explained
IOM guidelines: Institute of Medicine recommendations for total pregnancy weight gain, set differently depending on pre-pregnancy BMI category and whether the pregnancy is singleton or twin.