Child Growth Velocity Calculator

How to use

1. Enter the birth date and sex.
2. Enter the two height measurements and their dates.
3. Read the annual growth velocity and its verdict.
4. Note that a three-to-six-month gap is what makes the figure meaningful.

How it works

Why velocity only, no standard table

First, why this site doesn't do a "standard height table": height-percentile value tables are data-table standards that must follow the original text of China's WS/T 423-2022 and WS/T 612-2018. When building this tool, machine-readable, individually-verifiable Chinese standard tables weren't available, and a wrong "pass line" is worse than none — so it focuses on what pediatrics truly values: annual growth velocity. It needs few reference ranges, is verifiable item by item, and can reveal what a single height misses: a child with a moderate height now may already be falling behind because the velocity is dropping.

How annual growth velocity is computed and read

Annual growth velocity = (second height - first height) / interval days x 365.25, in cm/year. Example: a 7-year-old boy at 124 cm a year ago and 130.5 cm today, 365 days apart, gives 6.5 / 365 x 365.25 = about 6.5 cm/year, within the 4-8 cm/year reference for ages 4 to pre-puberty. A 3-6 month interval is advised (the tool limits it to 14-800 days): too short amplifies measurement error into tens of cm/year, too long misses mid-interval changes.

How to measure at home accurately

Reference ranges are tiered by age and sex: 20-30 at 0-1 year, 8-12 at 1-2, 5-9 at 2-4, 4-8 from 4 to pre-puberty, 7-12 for pubertal boys (from 11) and 6-11 for girls (from 10), and 0-2 after 16. The pubertal onset is distinguished by sex because girls are usually 1-2 years earlier. These are general references with wide individual variation: the value of assessment is spotting "clearly slow" — under 4 cm/year after age 4, height persistently below the 3rd percentile for same age and sex, or a percentiles consistently sliding down — which all warrant early evaluation of bone age and thyroid function.

Calculation basis: growth velocity = height gain ÷ days between measurements × 365.25. Reference ranges are banded by age and sex (20–30 cm/year at 0–1, 8–12 at 1–2, 5–9 at 2–4, 4–8 from age 4 to puberty, 7–12 for boys / 6–11 for girls in puberty, 0–2 after 16). The flags for seeking medical advice follow widely published paediatric guidance: growth under 4 cm/year after age 4, height below the 3rd percentile for age and sex, or a percentile that keeps sliding down the curve. The ranges are general guidance, individual variation is wide, and this is not a diagnosis.

Code example

function growthRate(h1Cm, d1, h2Cm, d2) {
  const days = (new Date(d2) - new Date(d1)) / 86400000;
  const cm = h2Cm - h1Cm;
  return {
    intervalDays: days,
    totalCm: cm,
    perYear: cm / days * 365.25          // annualised growth rate
  };
}

// School-age growth is about 5~7cm a year; during puberty girls 7~8cm and boys 8~10cm
growthRate(120, "2025-03-01", 124, "2025-09-01");   // ≈ 8.1cm/year

from datetime import date

def growth_rate(h1, d1, h2, d2):
    days = (d2 - d1).days
    return {"days": days, "cm": h2 - h1,
            "per_year": (h2 - h1) / days * 365.25}

growth_rate(120, date(2025, 3, 1), 124, date(2025, 9, 1))
# School-age reference is 5~7cm/year; measure at 3~6 month intervals

FAQ