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Pregnancy BMI Calculator
Calculate your pre-pregnancy BMI by WHO classification and see recommended weight gain per IOM 2009.
| BMI | Category | Rec. gain (singleton) |
|---|---|---|
| < 18.5 | Underweight | 12.5–18 kg |
| 18.5–24.9 | Normal weight | 11.5–16 kg |
| 25–29.9 | Overweight | 7–11.5 kg |
| ≥ 30 | Obese | 5–9 kg |
How it works
BMI uses the standard formula: weight (kg) ÷ height² (m). Use your weight BEFORE pregnancy. Weight-gain ranges follow the Institute of Medicine (IOM 2009) guidelines, the global standard. Conditions like gestational diabetes may shift individual targets.
Frequently Asked Questions
Which weight should I use for pregnancy BMI?+
Your weight BEFORE pregnancy. That number sets the recommended total gain per IOM 2009. Current pregnancy weight is not used here.
Why does pre-pregnancy BMI matter?+
It drives the recommended gain. Underweight women should gain more, women with obesity less — both reduce risks of preterm birth, gestational diabetes, and preeclampsia.
What if my BMI sits on a boundary?+
If your BMI is close to a category cutoff (e.g. 24.8 or 25.2), talk to your OB/GYN. Muscle mass, history, and individual risks can move the target.
Is the IOM 2009 guideline used worldwide?+
Yes. IOM 2009 is the global reference and uses WHO BMI categories. National guidelines (NICE, ACOG, DGGG) align with these ranges.
How does it differ for twins?+
BMI categories are the same. Total recommended gain is higher: 17–25 kg (normal), 14–23 kg (overweight), 11–19 kg (obese). Underweight twins use the singleton range.
My BMI is over 30 — what does that mean?+
Pregnancy with obesity carries higher risks (gestational diabetes, preeclampsia, cesarean). A modest gain of 5–9 kg reduces those risks. Closer prenatal monitoring is advised.
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Background
Pregnancy BMI Calculator — Pre-Pregnancy BMI & IOM 2009
7 min