BMI in Pregnancy Calculator

Health

Work out your pre-pregnancy BMI and see the recommended weight gain for a healthy pregnancy. Enter your pre-pregnancy weight and height, and this calculator returns your BMI, its category, and the Institute of Medicine (IOM) total weight-gain range for a single baby.

Rates and fees change frequently. Always confirm the current figures with the official authority before relying on this result.

Formula

BMI = pre-pregnancy weight (kg) ÷ height (m)² Recommended gain set by IOM category band
  • Use your weight from before pregnancy, since the recommendations are based on pre-pregnancy BMI.
  • BMI is your pre-pregnancy weight in kg divided by your height in metres squared.
  • IOM total weight-gain ranges for a single baby: underweight 12.5–18 kg, normal 11.5–16 kg, overweight 7–11.5 kg, obese 5–9 kg.
  • Twin pregnancies have higher recommended ranges and are not covered by these single-baby figures.
  • Healthy gain is gradual — most happens in the second and third trimesters. Always follow your own care provider's advice.

65 kg, 1.65 m before pregnancy

Inputs
  • Pre-pregnancy weight (kg): 65
  • Height (m): 1.65

BMI = 65 ÷ 1.65² ≈ 23.9 (normal weight), so the recommended total weight gain is about 11.5–16 kg over the pregnancy.

Frequently asked questions

Which weight should I enter?
Use your weight from just before pregnancy. The recommended weight gain is based on your pre-pregnancy BMI.
How much weight should I gain in pregnancy?
It depends on your starting BMI. IOM guidance suggests 11.5–16 kg for a normal BMI, more if underweight, and less if overweight or obese.
Why does BMI affect recommended weight gain?
Starting at a higher or lower weight changes the healthy amount to gain for you and your baby, so the target range is tied to your pre-pregnancy BMI.
Is this valid for twins?
No. These ranges are for a single baby. Twin and multiple pregnancies have higher recommended gains — ask your provider.
Should I diet to lose weight while pregnant?
Pregnancy is not the time for weight-loss dieting. Focus on balanced nutrition and follow your healthcare provider's guidance.