Pregnancy Weight Gain Calculator (IOM Guidelines)
Enter your pre-pregnancy height and weight to see the recommended weight gain.
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Pregnancy Weight Gain Calculator (IOM Guidelines) by TheCalcTools
How the Pregnancy Weight Gain Calculator (IOM Guidelines) works
The 2009 Institute of Medicine (now National Academy of Medicine) guidelines set total gain by pre-pregnancy BMI: underweight 12.5–18 kg, normal 11.5–16 kg, overweight 7–11.5 kg and obese 5–9 kg for a single baby, with higher ranges for twins.
Most of the gain happens after the first trimester (about 0.5 to 2 kg in the first 13 weeks). The weekly rates apply to the second and third trimesters. Your midwife or doctor may advise differently.
The formula
Worked example
Using the default values shown in the calculator:
| Pre-pregnancy weight | 62 |
|---|---|
| Height | 165 |
| Pregnancy | Single baby |
| Weeks pregnant now | 20 |
- BMI 22.8 (normal): gain 11.5 to 16.0 kg (25 to 35 lb).
- From week 14: 0.35 to 0.50 kg per week.
Result:
| Recommended total gain | 11.5 to 16.0 kg (25 to 35 lb) |
|---|---|
| Weekly gain in the 2nd and 3rd trimesters (single baby) | 0.35 to 0.50 kg per week |
| Pre-pregnancy BMI | 22.8 |
| Typical gain by this week (single baby, approx.) | 3.9 to 5.5 kg |
Frequently asked questions
Is it harmful to gain less?
Gaining far less or far more than recommended is linked to complications. Discuss your progress at antenatal visits rather than dieting in pregnancy.
Sources and further reading
- Institute of Medicine (2009): Weight Gain During Pregnancy: Reexamining the Guidelines
- CDC: Weight gain during pregnancy
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.