Growth Chart Calculator for Kids (CDC, 2–20 Years)

What a growth chart is for

A growth chart is a picture of how a large group of children grew, drawn as a set of curves by age. Each curve marks a percentile: the 50th is the median, the 5th marks the height that 5 percent of children are below, and so on. Plotting your own child's measurements on those curves turns a single number into context. More importantly, plotting several measurements over time shows the pattern of growth, which tells a doctor far more than any single visit.

The tool above plots height-for-age and weight-for-age on the CDC 2000 growth charts for boys and girls aged 2 to 20, in metric or US units. You can add as many measurements as you like (one per age), and each gets its own percentile and z-score in the table. The measurements live only in your browser tab and are never uploaded. This guide explains where the curves come from, which chart to use at which age, how fast children typically grow, how to tell a normal pattern from one worth discussing with a doctor, and how to measure accurately at home.

Where the CDC curves come from

The CDC charts replaced the 1977 NCHS growth charts in 2000. According to the 2002 methods report by Robert Kuczmarski and colleagues at the National Center for Health Statistics, the charts for older children were built from five national health examination surveys of US children conducted between the 1960s and 1990s, with supplementary data for infants. The empirical percentiles were smoothed in two stages and then summarized as three parameters for every month of age.

Those parameters, published in CDC's data files, are the heart of the chart:

• L, the power of a Box-Cox transformation, which corrects for skewness;
• M, the median;
• S, a generalized coefficient of variation, which captures spread.

CDC lists each value at the half-month point (for example, 96.5 months covers 96.0 to 96.99 months) and recommends interpolating between them for exact ages. Any percentile can then be calculated: the height at z-score Z is M × (1 + L·S·Z)^(1/L), and a measurement X converts back to a z-score with Z = ((X/M)^L − 1) ÷ (L·S). The tool draws the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th and 97th percentile curves from those formulas every three months of age, and computes each of your measurements at its exact age in months.

The CDC data files have not changed since May 2000, so every pediatrician, textbook and calculator that uses them is working from the same numbers.

Which chart to use at which age

Growth charts come in two broad types. A reference describes how a population actually grew; a standard describes how children should grow under good conditions.

• Under 2 years: US guidance, published by CDC in MMWR in 2010, recommends the WHO growth standards. They're based on the WHO Multicentre Growth Reference Study, which followed healthy, breastfed infants in Pelotas (Brazil), Accra (Ghana), Delhi (India), Oslo (Norway), Muscat (Oman) and Davis (California) between 1997 and 2003.
• 2 to 20 years: the CDC charts. Age 2 is a natural switch point because measurement changes from lying length to standing height, which already requires a new chart.
• Outside the US: many countries use national charts or the WHO references, including the WHO reference for ages 5 to 19 published in 2007, which reconstructs the 1977 NCHS/WHO data with modern statistical methods.

This tool starts at 24 months for that reason. If your 2-year-old was last measured lying down at the clinic, don't be surprised if a standing measurement at home doesn't line up exactly, because the two methods are not interchangeable.

How fast do children grow?

The CDC median curves also show how growth speed changes through childhood. The table below gives the yearly gain in median height, calculated from the CDC L-M-S data.

The pattern is the familiar one: fast growth in the toddler years, a steady 5 to 7 cm a year through middle childhood, a slowdown just before puberty, then a growth spurt. Girls' median gain peaks between 11 and 12; boys' between 13 and 14. By 15, the median girl is growing less than a centimeter a year, while the median boy still adds about 3.6 cm.

One caution: these are gains in the median across many children. Because every child starts the spurt at a different age, averaging smooths the spurts out. An individual teenager's peak year is usually faster than the median curve suggests, followed by a sharper slowdown. That's why a child can look as if they're "jumping" percentiles in early adolescence and then settle back.

Reading the pattern: steady tracking vs crossing lines

Healthy children usually follow a percentile channel. Here are two invented series of measurements for a boy, with percentiles calculated from the CDC curves:

Boy A drifts by a few points around the 50th percentile, which is completely normal. Boy B starts taller but grows only 10 cm in three years and falls from the 70th to the 18th percentile, crossing the 50th and 25th lines. Both boys are within the normal range at every single visit, yet only Boy B's pattern would prompt a doctor to look more closely. This is exactly why the tool lets you plot several measurements: one point can't reveal a trend.

Childhood height tracks adult height strongly but not perfectly. The Aberdeen Growth Study, published in 1956, was one of the first to quantify that tracking, which is why children who are far from average often drift partway back toward the middle as they grow.

Height-for-age and weight-for-age together

The tool can also plot weight-for-age. On its own, weight-for-age describes how heavy a child is compared with others of the same age. It doesn't account for height: a tall 10-year-old will naturally weigh more than a short one. The CDC median weight is 31.9 kg for a 10-year-old boy and 32.9 kg for a 10-year-old girl, reflecting girls' earlier puberty, and 70.6 kg and 58.2 kg at 20.

Looking at height and weight percentiles side by side is still informative. A child whose height and weight percentiles roughly match is usually growing in proportion. A weight percentile far above or below the height percentile is something to mention to the doctor, who will use BMI-for-age to assess weight for height properly.

A worked example, step by step

Here is exactly what the tool does when you enter a 10-year-old boy (120 months) who is 140.0 cm tall.

1. Look up L, M and S. CDC lists values at 119.5 and 120.5 months: L = 0.4997 and 0.5056, M = 138.41 and 138.82 cm, S = 0.04749 and 0.04761. Interpolating to 120.0 months gives L ≈ 0.5026, M ≈ 138.62 cm and S ≈ 0.04755.
2. Compute the z-score. (140.0 ÷ 138.62) is 1.00996; raised to the power 0.5026 it becomes 1.00499. Subtract 1 and divide by L × S (0.02390): z ≈ +0.21.
3. Convert to a percentile. A z-score of +0.21 corresponds to about the 58th percentile on the normal distribution.
4. Plot it. The point sits just above the 50th percentile curve, which at that age is the median of 138.6 cm.

The same steps run for weight-for-age with CDC's weight parameters. Because the tool interpolates to the exact month, a child measured at 9 years 11 months and again at 10 years 1 month gets two slightly different reference values, just as on a clinic chart.

Common mistakes with growth charts

• Using the wrong sex. Boys' and girls' curves diverge sharply after about age 10; a 13-year-old girl plotted on the boys' chart can look tall when she is average.
• Rounding the age. A child who is 7 years 11 months is almost 8. Entering "7" makes them look taller for their age than they are.
• Mixing shoes and bare feet. A sneaker adds about 2 cm, which can move a school-age child by 10 or more percentile points.
• Over-reading one point. A single reading near a line tells you little. Look for a sustained direction across at least three measurements spaced months apart.
• Comparing with siblings instead of curves. Siblings can be on quite different percentiles and both be perfectly healthy.

Measuring accurately at home

Growth over six months is only about 2.5 to 3.5 cm for a school-age child, so a half-centimeter error is a large fraction of what you're trying to see. Professional surveys use a careful protocol. In the US National Health and Nutrition Examination Survey, the child stands barefoot on a hard surface with heels together, toes pointed slightly outward, and the back of the head, shoulder blades, buttocks and heels touching the backboard. The head is positioned in the Frankfort plane, meaning the line from the ear canal to the lower edge of the eye socket is level, and the child takes a deep breath while the headpiece is lowered firmly onto the hair.

At home:

1. Remove shoes, hair clips and buns.
2. Use a wall without a baseboard and a hard floor, not carpet.
3. Lower a hardback book or a set square flat against the wall until it touches the crown.
4. Mark lightly, measure from the floor with a metal tape, and repeat; average two readings within 0.5 cm.
5. Measure at the same time of day each time, ideally in the morning. Height falls during the day as the spine settles: a 1986 study of adults in the British Journal of Sports Medicine recorded an average daily swing of 14.4 mm.

Normal variation and when to see a doctor

Children come in all sizes, and most who are small or tall are simply following their family pattern. Our World in Data notes that much of the stunting seen worldwide happens in the first two years of life, and that catch-up growth is possible when conditions improve, which is a reminder that height reflects nutrition and health as well as genes.

The CDC's 2010 guidance uses the 2.3rd and 97.7th percentiles (two standard deviations from the median) as screening thresholds, labeled on printed charts as the 2nd and 98th. The report explains that the 5th and 95th percentiles are arbitrary cut-offs that would flag too many healthy children as underweight or overweight, so a reading between the 3rd and 5th percentile is not by itself a cause for alarm. Talk to your child's doctor if you see:

• a measurement below the 3rd or above the 97th percentile curve;
• a fall or rise across two or more major percentile lines between check-ups;
• growth that stops or slows sharply, or puberty starting much earlier or later than in peers;
• a height far from what you'd expect from the parents' heights.

For a quick single check, use the height percentile calculator. To estimate a child's adult height from their current measurements and the parents' heights, try the height predictor. And to see how today's averages compare across 200 countries and a century of change, browse average height by country. If you'd like to see how much your child has grown in a more visual way, add their current and earlier heights side by side in the height comparison chart, where each figure is drawn to exact scale.