Pregnancy Weight Gain Calculator — IOM Guidelines
Enter your pre-pregnancy weight, height and current gestational week to get your recommended total weight gain range (IOM 2009) and where you should be right now — with the option to enter your actual gain to see if you are on track.
Units
lb
in
weeks
lb
25 lb – 35 lb (11.3 kg – 15.9 kg) — Normal weight (BMI 18.5–24.9)
How does this calculator work?
Your recommended pregnancy weight gain depends on your pre-pregnancy BMI: 25–35 lb for normal weight, 15–25 lb for overweight, 11–20 lb for obese, 28–40 lb for underweight (IOM 2009, single pregnancy). Most of the gain happens in the second and third trimesters at about 0.5–1 lb per week depending on your BMI category.
Formula
How this is calculated
The calculator first computes your pre-pregnancy body-mass index (BMI) from your weight and height, then looks up the Institute of Medicine (IOM) 2009 recommended total gestational weight-gain range for your BMI category. These ranges — updated by IOM in 2009 and still cited by the American College of Obstetricians and Gynecologists (ACOG) — are: 28–40 lb for underweight (BMI < 18.5), 25–35 lb for normal weight (BMI 18.5–24.9), 15–25 lb for overweight (BMI 25–29.9), and 11–20 lb for obese (BMI ≥ 30).
For weekly tracking, the calculator uses a simplified linear model: about 2 lb is expected in the first trimester (weeks 0–13), then roughly 1 lb per week for normal and underweight women, 0.6 lb per week for overweight, and 0.5 lb per week for obese women, through the end of the third trimester. This gives an expected range at your current week. If you enter your actual weight gain so far, the calculator compares it to that range and flags whether you are on track, below, or above.
These are population-level guidelines — individual situations vary widely. Twin or multiple pregnancies have different targets (IOM recommends 37–54 lb for twins at normal BMI). Medical conditions, morning sickness, gestational diabetes and other factors can change what is appropriate for you. Always follow the advice of your midwife or obstetrician.
Frequently asked questions
According to IOM 2009 guidelines: 28–40 lb if underweight (BMI < 18.5), 25–35 lb if normal weight (BMI 18.5–24.9), 15–25 lb if overweight (BMI 25–29.9), and 11–20 lb if obese (BMI ≥ 30). These values are for single pregnancies; twins and higher multiples have different ranges.
Some weight gain is necessary for a healthy pregnancy. For obese women (BMI ≥ 30), the IOM recommends a minimum of 11 lb gain. Trying to stay at exactly your pre-pregnancy weight is generally not recommended. Talk to your provider if you are concerned about weight gain.
The first trimester typically sees minimal weight gain (roughly 1–4 lb) as the embryo is tiny. In the second and third trimesters, the baby, placenta, amniotic fluid, blood volume and breast tissue all grow substantially, accounting for most of the recommended total gain.
Also known as
TG we-Calculate Editorial Team. (2026). Pregnancy Weight Gain Calculator — IOM Guidelines [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/how-to-maintain-weight-in-pregnancy-calculator
TG we-Calculate Editorial Team. "Pregnancy Weight Gain Calculator — IOM Guidelines." TG we-Calculate. 2026. https://we-calculate.com/calculator/how-to-maintain-weight-in-pregnancy-calculator.
TG we-Calculate Editorial Team, "Pregnancy Weight Gain Calculator — IOM Guidelines," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/how-to-maintain-weight-in-pregnancy-calculator
@misc{wecalculate_how_to_maintain_weight_in_pregnancy_calculator, title = {Pregnancy Weight Gain Calculator — IOM Guidelines}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/how-to-maintain-weight-in-pregnancy-calculator}}, year = {2026}, note = {TG we-Calculate} }
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