Pregnancy Weight Gain Calculator — IOM Recommended Range
Enter your pre-pregnancy weight and height to get the IOM 2009-recommended total weight gain range for your BMI category — including a trimester breakdown, weekly rate target, and a projected week-by-week growth curve.
Unit system
lb
in
Pregnancy type
25 – 35 lb — Normal weight (BMI 18.5–24.9)
- 1
Weight in kg
140 lb ÷ 2.205 = 63.5 - 2
Height in metres
65 in × 0.0254 = 1.651 - 3
Pre-pregnancy BMI
63.5 ÷ 1.651² = 23.3Determines which IOM 2009 weight-gain range applies. - 4
IOM minimum gain (Normal weight (BMI 18.5–24.9))
25Minimum of the recommended range from IOM 2009 singleton guidelines for this BMI category.
How does this calculator work?
IOM 2009 recommendations: underweight 28–40 lb, normal 25–35 lb, overweight 15–25 lb, obese 11–20 lb (singleton). Most gain happens in the 2nd and 3rd trimesters at 0.4–1.3 lb/week depending on BMI. Twins require significantly more: 25–54 lb depending on BMI category.
Formula
How this is calculated
The 2009 Institute of Medicine (IOM) report "Weight Gain During Pregnancy" established the pregnancy weight-gain guidelines most widely cited today. They are based on pre-pregnancy BMI, which this calculator computes from your weight and height. The four BMI categories — underweight (< 18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥ 30) — each have a recommended total gain range, a typical first-trimester gain, and a recommended weekly rate for the second and third trimesters.
The week-by-week growth curve is modelled as a linear ramp of about 2 lb in the first trimester, then a steady weekly gain thereafter — a simplified approximation of the IOM's tiered model. Real weight gain in pregnancy is uneven: nausea often suppresses gain in early weeks, while the third trimester sees rapid fetal growth. The curve gives a rough trajectory, not a prescription to hit each data point.
For twin pregnancies, the IOM recommends higher ranges: 37–54 lb for normal-weight women, 31–50 lb for overweight, and 25–42 lb for obese. Triplet guidelines are outside the IOM 2009 scope — consult your obstetric team. These are population-level starting points; individual advice from your midwife or doctor takes precedence.
Frequently asked questions
IOM 2009 recommends 25–35 lb (11–16 kg) for women with a pre-pregnancy BMI of 18.5–24.9. Most of this gain happens in the second and third trimesters at about 0.8–1.0 lb per week.
Timing matters somewhat. First-trimester gain is typically low (1–4 lb) as the embryo is tiny. The second and third trimesters account for the bulk of recommended gain as the baby, placenta, amniotic fluid, blood volume and breast tissue all grow substantially. Rapid large gains in any trimester can signal complications and should be discussed with a care provider.
No. Even women with obesity are expected to gain some weight in pregnancy (IOM recommends 11–20 lb, or 5–9 kg). Intentional calorie restriction during pregnancy is not advised without medical supervision, as it can affect fetal growth and nutrient supply.
Also known as
TG we-Calculate Editorial Team. (2026). Pregnancy Weight Gain Calculator — IOM Recommended Range [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/pregnancy-weight-gain-calculator
TG we-Calculate Editorial Team. "Pregnancy Weight Gain Calculator — IOM Recommended Range." TG we-Calculate. 2026. https://we-calculate.com/calculator/pregnancy-weight-gain-calculator.
TG we-Calculate Editorial Team, "Pregnancy Weight Gain Calculator — IOM Recommended Range," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/pregnancy-weight-gain-calculator
@misc{wecalculate_pregnancy_weight_gain_calculator, title = {Pregnancy Weight Gain Calculator — IOM Recommended Range}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/pregnancy-weight-gain-calculator}}, year = {2026}, note = {TG we-Calculate} }
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