Pregnancy Weight Gain — IOM 2009
Calculate recommended pregnancy weight gain based on pre-pregnancy BMI. IOM 2009 guidelines for singleton and twin pregnancies. Free, instant.
CalcVita. (2026). Pregnancy Weight Gain — IOM 2009. CalcVita. Retrieved June 3, 2026, from https://calcvita.com/en/calculators/pregnancy-weight-gain
Suggested article
Pregnancy Weight Gain: Evidence-Based Targets by BMI (IOM 2009)
How much weight should you gain during pregnancy? The IOM 2009 guidelines set evidence-based targets based on your pre-pregnancy BMI. Learn the ranges, weekly rates, and where the weight actually goes.
Read the full article →How is recommended weight gain calculated?
Enter your pre-pregnancy weight, height, and current gestational week. Select singleton or twin pregnancy. The calculator applies IOM 2009 guidelines to show your total recommended gain range and your expected gain at the current week.
IOM 2009 recommended weight gain ranges
| BMI category | Singleton | Twins |
|---|---|---|
| Underweight (< 18.5) | 12.5–18 kg | — |
| Normal (18.5–24.9) | 11.5–16 kg | 17–25 kg |
| Overweight (25–29.9) | 7–11.5 kg | 14–23 kg |
| Obese (≥ 30) | 5–9 kg | 11–19 kg |
Weight gain by trimester
First trimester (weeks 1–12): 0.5–2 kg total. Second and third trimesters: steady weekly gain based on your BMI category — from ~0.17 kg/week (obese) to ~0.58 kg/week (underweight).
Accuracy and limitations
These ranges are population-level recommendations. Individual needs vary based on multiple pregnancies, maternal health conditions, and other factors. Always follow your healthcare provider's personalised advice. (ACOG, 2013)
Scientific sources
- Institute of Medicine / National Research Council (2009). Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: The National Academies Press. doi:10.17226/12584
- American College of Obstetricians and Gynecologists (2013, reaffirmed 2022). Weight Gain During Pregnancy. Committee Opinion 548. acog.org
- Rasmussen KM, Yaktine AL, eds. (2009). IOM Report. ncbi.nlm.nih.gov/books/NBK32813
- How much weight should I gain during pregnancy?
- Recommended weight gain depends on your pre-pregnancy BMI per IOM 2009 guidelines: Underweight (BMI < 18.5): 12.5–18 kg (28–40 lb). Normal (18.5–24.9): 11.5–16 kg (25–35 lb). Overweight (25–29.9): 7–11.5 kg (15–25 lb). Obese (≥ 30): 5–9 kg (11–20 lb). These ranges are for singleton pregnancies. (Institute of Medicine, 2009. Weight Gain During Pregnancy. DOI: 10.17226/12584)
- How much weight should I gain with twins?
- For twin pregnancies, the IOM 2009 recommends: Normal BMI: 17–25 kg (37–54 lb). Overweight: 14–23 kg (31–50 lb). Obese: 11–19 kg (25–42 lb). There are insufficient data for underweight women carrying twins. (IOM/NRC, 2009. Weight Gain During Pregnancy. DOI: 10.17226/12584)
- How is the recommended weight gain distributed by trimester?
- During the first trimester (weeks 1–12), the typical weight gain is about 0.5–2 kg (1–4 lb) total. From the second trimester onward, gain is more consistent: approximately 0.35–0.50 kg/week for normal-weight women, 0.23–0.33 kg/week for overweight women, and 0.17–0.27 kg/week for obese women. (IOM/NRC, 2009)
- Why is gestational weight gain important?
- Adequate weight gain supports the baby's growth, reduces the risk of low birth weight or preterm delivery (with too little gain), and lowers the risk of large-for-gestational-age babies and cesarean delivery (with excessive gain). Both too little and too much weight gain are associated with adverse outcomes. (ACOG Committee Opinion 548, 2013)
- Does BMI before pregnancy affect how much I should gain?
- Yes. Women with a lower pre-pregnancy BMI need to gain more weight to support a healthy pregnancy, while women with a higher BMI can gain less. This is because the guidelines take into account the baby's needs and the mother's existing body reserves. Always discuss your individual target with your healthcare provider. (IOM/NRC, 2009)
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