Calculate weight-for-age percentile for children aged 2 to 20 with the official CDC 2000 LMS parameters, plus the median weight and why BMI matters more.
| Input | Result |
|---|---|
| 10-year-old boy, 32 kg | about the 50th percentile |
| 10-year-old girl, 32 kg | about the 55th percentile |
| 5-year-old boy, 18 kg | about the 45th percentile |
| 15-year-old boy, 55 kg | about the 38th percentile |
A growth percentile compares your child with a reference population of the same age and sex — not with "normal". The 50th percentile is the median, not a target. A healthy child can sit steadily at the 10th percentile for years, and that is a different situation from a child who drops from the 60th to the 10th in six months.
This is why pediatric practice looks at the curve, not the number. A single measurement tells you where a child is; two or three measurements over time tell you how they are growing, which is the thing that actually carries information. Very few children track a constant percentile — most move up or down one band between visits and that is normal.
| Measure | What it accounts for | Best used for |
|---|---|---|
| Weight-for-age | Age and sex only | Tracking growth in early childhood and flagging underweight |
| BMI-for-age | Age, sex and height | The recommended screening measure from age 2 through 20 |
A tall, muscular child can sit high on weight-for-age while having a perfectly healthy BMI; a short child can sit low while carrying excess body fat. That is why pediatric offices stop leaning on weight-for-age once a child turns two.
These are the reference values themselves, not estimates: the M column of the CDC LMS file is the 50th percentile, so this table is the published median for each age and sex. Whole-year ages are interpolated between the published monthly rows.
| Age | Boys | Girls |
|---|---|---|
| 2 years | 12.7 kg | 12.1 kg |
| 3 years | 14.3 kg | 13.9 kg |
| 4 years | 16.2 kg | 15.8 kg |
| 5 years | 18.4 kg | 17.9 kg |
| 6 years | 20.7 kg | 20.2 kg |
| 7 years | 23.1 kg | 22.8 kg |
| 8 years | 25.6 kg | 25.6 kg |
| 9 years | 28.6 kg | 29.0 kg |
| 10 years | 31.9 kg | 32.9 kg |
| 11 years | 35.9 kg | 37.2 kg |
| 12 years | 40.5 kg | 41.6 kg |
| 13 years | 45.6 kg | 45.8 kg |
| 14 years | 51.0 kg | 49.4 kg |
| 15 years | 56.3 kg | 52.0 kg |
| 16 years | 60.9 kg | 53.9 kg |
| 17 years | 64.6 kg | 55.1 kg |
| 18 years | 67.2 kg | 56.2 kg |
| 19 years | 69.1 kg | 57.3 kg |
| 20 years | 70.6 kg | 58.2 kg |
The reference values come from the CDC 2000 growth charts, published by the US Centers for Disease Control and Prevention. The CDC publishes them as LMS parameters, which are the official way to describe a growth distribution that is skewed rather than normally distributed. From the three parameters:
M is the median (the 50th percentile value), S is the coefficient of variation and L is the skewness power that bends the distribution into the right shape. The percentile is then the standard normal cumulative distribution at z: percentile = Φ(z) × 100.
Age is interpolated linearly between the published half-month rows, then rounded to the nearest half month. Interpolation in the middle of a 0.5-month gap introduces far less error than the measurement error of a home height or weight reading, which is typically 0.5–1 cm and 0.1–0.2 kg.
| Age | Correct reference | Why |
|---|---|---|
| 0–2 years | WHO growth standards | CDC and the AAP recommend WHO charts for under-2s because they describe how healthy, breastfed infants grow rather than how a mixed US sample grew. |
| 2–20 years | CDC 2000 growth charts | The reference used on this page, and the one US pediatric offices plot against past age 2. |
Mixing the two produces a visible step at age 2, which is exactly the artefact the CDC warns about. If your child is close to that boundary, keep every measurement on the same chart.
It shows how a child's weight compares with other children of the same age and sex. It is useful for tracking growth over time, but it cannot distinguish muscle from fat, which is why the CDC recommends BMI-for-age for children aged 2 and over.
Because weight-for-age alone can mislead in both directions: a tall, muscular child can sit high on weight-for-age while having a healthy BMI, and a short child can sit low while carrying excess fat. BMI-for-age combines height and weight and is the recommended screening measure from age 2.
Weight gain is not linear. Children typically gain around 2 kg (4–5 lb) per year between ages 2 and 5, then roughly 2.5–3.5 kg per year through the school years, with a faster pubertal growth spurt. A single year outside the pattern is less informative than the trend over three.
Below the 5th percentile is conventionally called underweight, and below the 3rd is a common referral threshold. It is a reason for a pediatric conversation, not a diagnosis — some children are simply constitutionally small and growing normally.
No. The CDC 2000 charts used here cover ages 2–20; for under-2s, CDC and the AAP recommend the WHO growth standards.