Calculate a baby's body mass index from weight and height and see a rough age-based band. BMI for babies must be read on a WHO BMI-for-age chart by age and sex. This is an approximate reference, not medical advice and not a diagnosis; for any health concern or emergency, contact your pediatrician or emergency services, and follow WHO, CDC or your local health authority guidance.
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How to Use the Baby BMI Calculator
Enter the age in months, weight and height, then press Calculate BMI. The tool works out BMI and a rough band for the age.
Reading the result
BMI is weight in kilograms divided by height in metres squared.
Babies naturally have a higher BMI than older children, and it changes quickly in the first year.
BMI must be plotted on a WHO BMI-for-age chart for your baby's age and sex.
A single value matters less than the trend over time.
Features
BMI from weight and height
A rough age-based band for quick context
Reminder that official charts use age and sex
This is an approximate reference, not medical advice and not a diagnosis; for any health concern or emergency, contact your pediatrician or emergency services, and follow WHO, CDC or your local health authority guidance.
All processing runs locally in your browser. Your data is not uploaded to any server.
If you are concerned about your baby's weight or growth, speak to your pediatrician, who can measure and plot it properly.