BMI for kids works differently than for adults

For adults, BMI has fixed cutoffs (25 is "overweight" and so on). For children those numbers mean nothing, because healthy body composition changes constantly as kids grow. A perfectly healthy 5-year-old can have a BMI of 14 — a number that would signal severe underweight in an adult.

It's the percentile that talks

A child's BMI is compared with children of the same age and sex. Under the 5th percentile suggests underweight; 5th–85th is the healthy range; 85th–95th flags overweight; above the 95th, obesity. These are screening bands, not diagnoses — a stocky, athletic kid can sit above the 85th with nothing wrong at all.

The adiposity rebound (worth knowing)

BMI normally falls through toddlerhood, bottoms out around age 5–6, then rises again — that upturn is called the adiposity rebound. It's one reason single measurements mislead: the direction and timing of the curve carries more information than any one point.

What to do with the number

Nothing dramatic. If the percentile is drifting steadily upward across visits, look at the usual suspects — sugary drinks, screen-heavy days, short sleep — and raise it at the next check-up. Never put a preschooler on a "diet" on your own; growing bodies need energy, and the goal is habits, not weight loss.