How the growth velocity calculator works
Velocity over percentiles
Growth charts show position; velocity shows direction. Expected rates fall steeply from infancy (~10 in/year) through childhood (~2.5), dip pre-puberty, spike at puberty (3–4), and taper to zero as growth plates close. A child whose velocity matches age expectations is growing healthily at any percentile — and a child whose velocity stalls, at any percentile, is the one the pediatrician wants to see.
The measurement error problem
Home height measurements carry ±0.25–0.5 inch of technique error — over a 6-month window that can double or erase an apparent growth rate. The mitigations: hard floor and wall, level book or ruler on the head, same time of day (we are ~0.5 inch taller in the morning), and measuring over at least 6 months so the signal outruns the noise.
When velocity raises flags
Falling below ~1.5–2 in/year in mid-childhood, crossing below the pre-pubertal dip too early, or a sharp deceleration all warrant evaluation — thyroid, celiac, growth hormone, and chronic disease are the standard screens. The majority of slow-velocity workups end in "constitutional" (genetically slow, healthy) — but the finding belongs to a professional, not a calculator.