Weight Percentile Calculator for Children & Teens (CDC, 2–20 years)

Understanding the weight percentile calculator for children and teens — concept and principle

This calculator compares a child's or teenager's weight with children of the same age and sex using the CDC 2000 weight-for-age chart for ages 2 to 20. It gives the percentile, z-score and the 5th, 50th and 95th percentile weights.

CDC LMS curve: with the default inputs the result is 56.1 (weight percentile).

How it is calculated

z = ((weight ÷ M)^L − 1) ÷ (L × S)

Percentile = share of the normal distribution below z

Weight at a percentile = M × (1 + L × S × z)^(1/L)

L, M and S come from the CDC table for the child's sex and age (taken at the middle of the month, interpolated between table ages).

The principle

Children's weights at a given age are skewed: there is a longer tail towards heavier weights. The LMS method uses the L value to transform the distribution into a normal one, so a z-score and percentile can be calculated. M is the median and S the spread. The percentile is the share of reference children of the same age and sex who weighed less.

Worked example

Default inputs: boy, 10 years 0 months, 33 kg.

Age = 120.5 months; CDC values L = −1.207, M = 32.09 kg, S = 0.1789.
z = ((33 ÷ 32.09)^−1.207 − 1) ÷ (−1.207 × 0.1789) = 0.15.
Percentile = 56.1; median 32.1 kg; difference 0.9 kg.
5th percentile 24.9 kg, 95th 46.2 kg.

Each point is the calculator re-run with only “Child’s weight (kg)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Child’s weight (kg)	Percentile
8.25	0
16.5	0
24.8	4.4
33	56.1
41.2	88.7
49.5	97
66	99.6

How to read the result

Where does your result fall?

Weight-for-age alone does not show whether a child is under- or overweight for their height; use BMI-for-age for that. The trend over time matters more than one value: crossing major percentile lines deserves a check. For babies under 2, the WHO standards are used.

Common mistakes

Using weight percentile to judge overweight instead of BMI-for-age.
Weighing with shoes and heavy clothes.
Rounding age to whole years.

Keep in mind: This is not a diagnosis. Discuss your child's growth with a doctor.

Frequently asked questions

What weight percentile is normal?

Most children fall between the 5th and 95th; steady growth along a curve matters more.

Why is the 95th percentile so far above the median?

Weight distributions are skewed towards heavier values.

Should I use this or BMI?

Use BMI-for-age to judge weight relative to height.

Sources: Kuczmarski RJ et al., "2000 CDC Growth Charts for the United States: Methods and Development", Vital Health Stat 11(246), 2002

Checked 9 Nov 2026. CDC 2000 growth charts, weight-for-age LMS parameters, 2–20 years (Kuczmarski RJ et al., Vital Health Stat 11(246), 2002). LMS values as distributed in the RCPCH rcpchgrowth package.

Your numbers