Growth percentiles tell you how a child's height or weight compares to other children of the same age and sex. They are a key tool in paediatric medicine for tracking development over time.

What Percentiles Mean

If a child is at the 75th percentile for height, they are taller than 75% of children their age and shorter than 25%.

No single percentile is "correct" — what matters is consistency over time. A child following the 10th percentile is growing normally; crossing from the 50th to the 10th is a warning sign.

UK Growth Charts (WHO/RCPCH)

UK uses WHO standards for children 0–4, then UK90 charts from age 4:

Boys' height at age 2:

PercentileHeight
2nd82.5 cm
9th85.0 cm
25th87.0 cm
50th88.5 cm
75th90.5 cm
91st92.0 cm
98th94.5 cm

Calculating Height Percentile (Z-Score Method)

Z-score = (Child's measurement − Mean for age/sex) ÷ SD for age/sex

Look up reference mean and SD in WHO growth tables, then convert z-score to percentile.

Example: A 4-year-old girl is 103 cm tall. Reference: mean = 101.3 cm, SD = 4.0 cm:

Z = (103 − 101.3) ÷ 4.0 = 0.425
Percentile ≈ 66th

Predicted Adult Height

Mid-parental height (MPH):

For boys:

MPH = (Father's height + Mother's height + 13 cm) ÷ 2

For girls:

MPH = (Father's height + Mother's height − 13 cm) ÷ 2

Target range = MPH ± 8.5 cm (captures ~95% of children).

Example: Dad 175 cm, Mum 163 cm, predicting for a son:

MPH = (175 + 163 + 13) ÷ 2 = 351 ÷ 2 = 175.5 cm
Target range: 167–184 cm

BMI for Children

Unlike adults, child BMI uses age- and sex-specific percentiles, not fixed thresholds:

BMI percentileCategory
Below 2ndUnderweight
2nd–85thHealthy weight
85th–95thOverweight
Above 95thObese

Adult BMI categories (18.5, 25, 30) are not used for children under 18.

When to Seek Medical Advice

  • Child crosses 2 major centile lines downward
  • Height below 2nd or above 98th percentile
  • Sudden acceleration or slowing of growth
  • BMI consistently above 91st percentile

Growth is reviewed at the 6-week, 8-month, and 2-year health visitor checks in the UK.