Child Growth Percentile Calculator

Choose Boy, set age to 8 years and 0 months (96 months), and enter a weight of 25.5 kg and a standing height of 128 cm. You can switch to pounds and inches; the calculator converts to kilograms and centimetres before looking anything up.

For weight, the calculator reads the CDC values for boys at 96 months: a median (M) of 25.64 kg, with L = −1.349 and S = 0.1556. The weight of 25.5 kg is just under that median, giving z = −0.04 and the 48.6th percentile, between the 25th and 50th percentile lines printed on the chart.

For height, the median at 96 months is 127.88 cm, so 128 cm gives z = 0.02 and the 50.8th percentile, between the 50th and 75th lines.

The calculator also shows the 5th, 50th and 95th percentile values at that age. For this boy, the 5th to 95th percentile weight range is 20.6 kg to 35.1 kg, and the height range is 118.6 cm to 137.6 cm. That spread is the most useful thing on the page for a worried parent: the range of ordinary eight-year-olds is very wide.

Reference data: the CDC 2000 growth charts for the United States, from the National Center for Health Statistics. The CDC publishes the chart values as data files: wtage.csv for weight-for-age and statage.csv for stature-for-age. This calculator stores both files' L, M and S columns exactly as published, for boys and girls, from 24 to 240 months.

Age lookup: the tables list values at exactly 24 months and then at each half month (24.5, 25.5, 26.5 and so on up to 239.5, then 240). For an age between two rows, L, M and S are interpolated linearly between the two nearest rows.

The LMS method: each age has a skewness parameter L, a median M and a coefficient of variation S. The z-score is z = ((X ÷ M)^L − 1) ÷ (L × S), a transformation described by T. J. Cole in 1990 that turns a skewed measurement into a normally distributed one. The percentile is Φ(z) × 100, where Φ is the standard normal cumulative distribution.

Percentile lines: the 5th and 95th percentile values shown come from inverting the formula, X = M × (1 + L × S × z)^(1/L), at z = ±1.645.

Checked against the CDC: the published files also list the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th and 97th percentile values for every row. Feeding each of those values back into this calculator returns the matching percentile to within 0.00001 of a percentile point, for every row of both files.

Choose Girl, set age to 14 years and 6 months (174 months), and enter 45 kg and 150 cm.

Weight comes out at the 23.8th percentile (z = −0.71), between the 10th and 25th lines. Height comes out at the 4.2nd percentile (z = −1.73), between the 3rd and 5th lines. The median height for girls of this age is 161.27 cm, so this girl is about 11.3 cm below it.

This is the kind of result that should be read carefully rather than alarmingly. Adolescence is when percentiles are least stable, because children go through their growth spurt at different ages. A girl who starts puberty later than average can sit low on the stature chart for a year or two and then climb back as she catches up. A girl who has already finished growing and sits at the same point will not.

The number cannot tell those two situations apart. Only the pattern over time can, along with information a pediatrician collects: signs of puberty, the parents' heights, earlier measurements and general health. If the same girl still measured 150 cm at 18, she would be at the 2.2nd percentile — and that single comparison makes clear why growth is judged as a trajectory.

Percentile lines are not targets. A child who has always tracked along the 10th percentile and continues to do so is growing consistently; being small is not in itself a problem. What prompts a closer look is a change in pattern, such as a child who moves steadily across the major percentile lines over several visits, or whose weight and height move in different directions.

Measurement technique matters as much as the numbers. Height should be measured standing, without shoes, back against a wall or stadiometer, looking straight ahead. Home measurements with a tape against a door frame can easily be off by a centimetre or more, which is enough to move a percentile several points. Weight changes during the day with meals and clothing.

The CDC recommends different charts for different ages. For children under 2 years, the CDC recommends the WHO growth standards, which describe how healthy breastfed infants grow; for ages 2 to 19, it recommends the CDC 2000 charts used here. That is why this calculator starts at 24 months.

Not a diagnosis. A percentile, high or low, does not mean a child is unwell, and a percentile in the middle does not rule anything out.

A reference, not a standard. The CDC 2000 charts describe how a sample of U.S. children grew in the decades the data came from. They show how children did grow, not how they ideally should grow.

Ages 2 to 20 only. Under 2, use the WHO growth standards through your pediatrician. The calculator will not return a result outside 24 to 240 months.

Not for all children. Children born very preterm and children with conditions that affect growth, such as Down syndrome, may need specialised charts. Ask the child's doctor which reference applies.

Weight-for-age does not describe body fat. A tall child will naturally be heavier. To judge weight relative to height, a BMI-for-age percentile is the appropriate measure.

This calculator gives weight-for-age and height-for-age. To judge whether a child's weight is proportionate to their height, use the kids BMI percentile calculator, which applies the CDC BMI-for-age data to classify weight status; the two pages answer different questions and are most useful together. For adults, weight relative to height is assessed with the adult BMI calculator instead of percentiles. Growth tracking starts before birth, too: the pregnancy calculator lays out the timeline of a pregnancy, and the gestational age calculator works out how far along a pregnancy is, which is also the basis for correcting a preterm baby's age on early growth charts.