Pregnancy Weight Gain Calculator
See the recommended total pregnancy weight-gain range for your pre-pregnancy BMI, plus a guide to how much to have gained by a given week.
How it works
Pre-pregnancy BMI = weight_kg ÷ height_m² · Total gain range set by BMI category (IOM 2009): underweight 12.5–18, normal 11.5–16, overweight 7–11.5, obese 5–9 kg
Recommended pregnancy weight gain depends on where you started: the Institute of Medicine guidelines set a wider range for those who began underweight and a narrower, lower range for those who began with a higher BMI. Most of the gain comes in the second and third trimesters — often only 0.5–2 kg in the first — reflecting the growing baby, placenta, fluid and blood volume. Gaining within your range is linked to healthier outcomes, but your own clinician tailors the target to your circumstances.
Worked example
A woman 165 cm and 62 kg before pregnancy has a BMI of 62 ÷ 1.65² = 22.8, which is normal weight, so the recommended total gain is 11.5–16 kg. By week 20 a typical range gained is roughly 3–6 kg.
Frequently asked questions
How much weight should I gain in pregnancy?
It depends on your pre-pregnancy BMI. IOM guidance recommends 12.5–18 kg if underweight, 11.5–16 kg if normal weight, 7–11.5 kg if overweight and 5–9 kg if obese, for a single baby.
When does most weight gain happen?
The first trimester usually adds little (about 0.5–2 kg). The steady gain comes in the second and third trimesters as the baby, placenta, blood and fluid grow.
What about twins?
Twin pregnancies call for more gain — commonly 17–25 kg for a normal-weight start. Your care provider sets an individual target for multiples.
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Educational estimate using standard formulas and population averages — not medical advice. Talk to a qualified clinician before making decisions about diet, training, or pregnancy.