Percentiles
Percentiles show how a child's height, weight and BMI compare with those of children the same age – they're the curves in Germany's yellow child health booklet.
Ausführlich erklärt
A percentile tells you what percentage of children of the same age and sex are shorter, lighter or slimmer than your child. If your child's height is on the 75th percentile, then out of 100 children in the comparison group, 75 are shorter and 25 are taller. Because children are still growing, a single figure like BMI says little on its own – it only becomes meaningful when compared by age and sex.
For BMI, paediatricians in Germany use the Kromeyer-Hauschild reference curves (2001), which are also recommended in the guideline of the German Working Group on Obesity in Childhood and Adolescence (AGA): a BMI above the 90th percentile counts as overweight, above the 97th percentile as obesity and below the 10th percentile as underweight. The WHO uses its own curves and so-called z-scores, which reflect the same principle.
Height and weight are measured at every routine check-up – from the U1 straight after birth and the U9 at around five years to the J1 at 12 to 14 years. The curves for the first years of life are in the yellow child health booklet. What matters is less the individual point than the trend: a child who stays steadily on “their” curve for years is developing well, whether on the 20th or the 80th percentile. If, on the other hand, your child's line crosses two of the printed curves upwards or downwards, that's a reason to take a closer look.
For parents, this means: it's not the adult BMI calculator or a table from the internet but your child's paediatrician who assesses your child's weight. And a high value isn't a diagnosis – it's a reason for a calm conversation about physical activity, sleep, drinks and family meals.
From the age of about five, the waist-to-height ratio (WHtR) can also give a rough guide – and here too, interpreting it belongs in a doctor's hands.