BMI-for-Age Calculator

For children, BMI only means something next to their age and sex, because healthy body fat changes so much as they grow. That is why doctors use BMI-for-age percentiles rather than the adult cut-offs of 18.5 and 25.

How it works

BMI is weight in kilograms divided by height in metres squared. The calculator then places that BMI on the WHO BMI-for-age standard (birth to 5 years) or reference (5 to 19 years) for your child's sex and exact age, and reports the percentile and the WHO category. Under 5, WHO uses length lying down before 2 and height standing after.

Questions parents ask

What counts as a healthy BMI for a child?

Roughly the 15th to 85th percentile for age. WHO flags "possible risk of overweight" above the 85th, "overweight" above the 97th, and "thinness" below the 3rd, but a single reading is a prompt for a conversation with your doctor, never a diagnosis.

Why is my toddler's BMI lower than a baby's?

Because that is normal. BMI peaks around 9 to 12 months, falls until about 5 or 6 years, then rises again (the "adiposity rebound"). Percentiles for age take this into account; the raw BMI number on its own does not.

Should I put my child on a diet?

No. For children, the goal is healthy habits and letting height catch up with weight, not weight loss, and any plan should come from a paediatrician or dietitian.

Sources

• WHO Child Growth Standards: BMI-for-age (2006)
• WHO Growth Reference 5-19 years: BMI-for-age (2007)

Bheeli offers general guidance, not medical advice.