Child Growth Chart Calculator

Child growth chart percentiles express where a child falls relative to the reference population of the same age and sex. A child at the 75th percentile for height is taller than 75% of children their age. That does not mean they are unhealthy, only that they are above average.

Percentile calculation (Z-score method): The CDC/WHO growth charts use the LMS method: Z = [(X ÷ M)^L − 1] ÷ (L × S)

Where:

• X = the child’s measurement (height in cm or weight in kg)
• M = median reference value for that age/sex
• L = Box-Cox power transformation parameter (corrects for skewness)
• S = coefficient of variation at that age/sex

The percentile is then read from a Z-score table (Z=0 → 50th percentile; Z=1 → 84th; Z=2 → 97.7th).

Simplified interpretation (without LMS tables): Most pediatricians use pre-computed growth charts from the CDC (US) or WHO (international under age 2). Plot the child’s measurement on the chart and read the percentile directly.

What each variable means:

• Percentile vs. absolute value: a 3-year-old at the 10th percentile is perfectly healthy as long as they track consistently along the 10th percentile line over time
• Growth velocity: the rate of growth over time is more important than a single measurement; crossing two major percentile lines (e.g. 75th to 25th) warrants investigation
• WHO vs. CDC charts: WHO charts (birth to age 2) are based on children raised in ideal conditions; CDC charts (age 2+) reflect the actual US population including overweight children

Reference: growth percentile categories:

• Below 3rd: Very low: medical evaluation recommended
• 3rd–15th: Low-normal: monitor closely
• 15th–85th: Normal range
• 85th–97th: High-normal: for weight, may signal overweight risk
• Above 97th: Very high: medical evaluation recommended

Worked example, the one this calculator runs: Boy, age 4.0 years. Height 104 cm, weight 17.5 kg.

The reference figures this page holds for a 4-year-old boy are a median height of 102 cm with a standard deviation of 4 cm, and a median weight of 16.3 kg with a standard deviation of 2 kg.

• Height: z = (104 − 102) ÷ 4 = 0.50, which reads off the normal curve at the 69th percentile
• Weight: z = (17.5 − 16.3) ÷ 2 = 0.60, which is the 73rd percentile
• Body Mass Index (BMI) = 17.5 ÷ 1.04² = 16.2, a healthy figure for this age

Slightly above average on both, and in proportion. What matters at the next checkup is not whether these numbers rise but whether they stay on the same lines.

A note on the reference data. This page carries a compact median-and-spread table rather than the full CDC L, M and S parameters, so the percentiles it prints are close to a plotted chart but not identical to one. Expect a couple of points of difference at the extremes, where the real distribution is skewed and a plain standard deviation is a rough stand-in. For anything clinical, use the chart your pediatrician plots.