Recommended Gestational Weight Gain Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/9/2026
Recommended weight gain during pregnancy depends on pre-pregnancy BMI: about 11.5 to 16 kg for a normal BMI (18.5-24.9), 12.5 to 18 kg if underweight, 7 to 11.5 kg if overweight, and 5 to 9 kg if obese (Institute of Medicine guidelines).
Explanation
The recommended weight gain range during pregnancy directly depends on the mother's body size before pregnancy, measured by her BMI (see our BMI calculator for this calculation, to be done before pregnancy). These benchmarks, established by the U.S. Institute of Medicine (IOM) in 2009 and widely adopted internationally, including by the American College of Obstetricians and Gynecologists (ACOG), follow a simple but important principle: the lower the starting BMI, the wider the recommended weight gain range, and vice versa. A woman who is underweight before pregnancy (BMI below 18.5) is given the most generous range, 12.5 to 18 kg, while a woman who is obese before pregnancy (BMI of 30 or above) is given a noticeably narrower range, 5 to 9 kg. Between these two extremes, a normal pre-pregnancy BMI (18.5 to 24.9) corresponds to a range of 11.5 to 16 kg, and an overweight BMI (25 to 29.9) to a range of 7 to 11.5 kg. These recommendations rest on data linking gestational weight gain to risks for both the mother (gestational diabetes, hypertension, delivery complications) and the baby (birth weight too low or too high), with weight gain within the recommended range associated with the best outcomes on average for both. These ranges remain general benchmarks established from large populations, not an individual prescription: prenatal care provided by a midwife or obstetrician-gynecologist remains the right setting for assessing a specific weight gain, particularly for a multiple pregnancy (twins or more), not covered by these benchmarks established for a single pregnancy. For the calorie intake associated with this weight gain, see our pregnancy calorie needs calculator.
Example: a pre-pregnancy BMI of 22 (normal weight)
Inputs
Pre-pregnancy BMI: 22.
Calculation
A BMI of 22 falls in the "normal weight" category (18.5 to 24.9), corresponding to a recommended range of 11.5 to 16 kg.
Result
For this starting BMI, the recommended weight gain during pregnancy falls between 11.5 and 16 kg.
Frequently asked questions
Why is the recommended range wider for underweight than for obese women?
Because a woman who is underweight before pregnancy starts with more limited energy reserves, which justifies a larger weight gain to healthily support the baby's development; conversely, a woman who is obese already has substantial energy reserves, which allows for more moderate gestational weight gain without compromising the baby's development, while limiting the risks associated with excessive weight gain for the mother.
Do these benchmarks apply to a twin pregnancy?
No, these ranges were established for a singleton pregnancy (one baby): a multiple pregnancy (twins or more) generally warrants a larger recommended weight gain, to be discussed specifically with the healthcare professional providing care for that particular pregnancy.
What happens if actual weight gain falls outside this range?
Weight gain outside the recommended range (too little or too much) is statistically associated with a slightly increased risk of certain complications, but is never a diagnosis or an emergency in itself: every pregnancy has its own particulars, and only the healthcare professional providing care (midwife, obstetrician-gynecologist) can assess a specific situation and adjust recommendations if needed.