What is a growth percentile?
A percentile shows where a measurement stands among 100 children of the same sex and age, using the WHO Child Growth Standards. A 62nd percentile for weight means the child weighs more than about 62 of 100 same-age, same-sex children — and less than about 38. A low percentile is not automatically bad, and a high one is not automatically good: what matters most is a steady, consistent growth pattern over time.
z = ((measurement / M)^L − 1) / (L × S), or z = ln(measurement / M) / S when L = 0. Percentile = Φ(z) × 100.
How the calculation works (LMS method)
- L, M, S — WHO reference values (skewness, median, coefficient of variation) for the child's exact age in days, sex and measurement type, found by linear interpolation between the nearest published days.
- z = 0 is exactly the 50th percentile; z = −2 is about the 2.3rd percentile; z = +2 is about the 97.7th percentile.
Limits of this calculator
This tool is for reference only and is not a medical diagnosis. A single measurement matters less than the trend across repeated measurements — talk to a pediatrician or health worker if a value looks unusual or a trend changes suddenly.
What does a growth percentile tell you?
A growth percentile compares your child's weight, height, or head circumference with WHO's global reference data for children of the same age and sex. It answers one question: among 100 typical children the same age, how many would be lighter, shorter, or have a smaller head than yours?
How to read your result
- Enter your child's sex and age — by date of birth and measurement date, or directly in months.
- Enter any combination of weight, height/length, and head circumference; you do not need all three.
- Read the percentile and z-score for each measurement you entered.
- Check the WHO median for that exact age to see how far above or below average the value is.
- Repeat at the next checkup and compare the trend, not just a single number.
The LMS method WHO uses
z = ((measurement / M)^L − 1) / (L × S), or z = ln(measurement / M) / S when L = 0. Percentile = Φ(z) × 100.
- L, M and S come from WHO's daily reference tables for the child's exact age in days, sex, and measurement type, using linear interpolation between the nearest published days.
- Φ is the standard normal cumulative distribution function — it converts a z-score into a percentage.
WHO reference values by age (boys)
| Age | Weight −2SD / median / +2SD (kg) | Height/length −2SD / median / +2SD (cm) | Head circumference −2SD / median / +2SD (cm) |
|---|
| Birth (0 mo) | 2.5 / 3.3 / 4.4 | 46.1 / 49.9 / 53.7 | 31.9 / 34.5 / 37.0 |
| 6 months | 6.4 / 7.9 / 9.9 | 63.4 / 67.6 / 71.9 | 40.9 / 43.3 / 45.8 |
| 12 months | 7.7 / 9.6 / 12.0 | 71.0 / 75.7 / 80.5 | 43.5 / 46.1 / 48.6 |
| 24 months — recumbent length | 9.7 / 12.1 / 15.3 | 81.7 / 87.8 / 93.9 | 45.5 / 48.2 / 51.0 |
| 24 months — standing height | 9.7 / 12.2 / 15.3 | 81.0 / 87.1 / 93.2 | 45.5 / 48.3 / 51.0 |
| 60 months (5 years) | 14.1 / 18.3 / 24.2 | 100.7 / 110.0 / 119.2 | 47.7 / 50.7 / 53.7 |
Frequently asked questions
What is a good percentile for a baby?
There is no single 'good' percentile — WHO considers roughly the 3rd to 97th percentile as the expected range for a healthy child. What matters more than any one number is that the child tracks along a fairly consistent percentile line over repeated measurements.
Why did my child's height percentile change at exactly 24 months?
WHO measures children under 2 as recumbent (lying) length and children 2 and older as standing height. Standing height is typically about 0.7 cm shorter than recumbent length at the same age, purely from posture — so a small drop in percentile right at 24 months is expected and not a growth problem.
Is a low percentile a sign of a problem?
Not by itself. Many healthy children track consistently in the lower percentiles their whole childhood. What a clinician looks for is a sudden drop across percentile lines (for example, from the 50th to the 10th) or a value below the 3rd percentile, not simply being on a low but stable line.
Can I use this for premature babies?
This calculator uses the standard WHO Child Growth Standards, built from full-term, healthy, breastfed infants. For babies born preterm, growth is usually tracked using corrected (adjusted) age rather than actual age, ideally with a pediatrician's guidance.
What's the difference between weight-for-age, height-for-age, and head-circumference-for-age?
Each compares a different measurement to the same-age, same-sex WHO reference: weight-for-age reflects overall body mass, height/length-for-age reflects linear growth over time, and head-circumference-for-age reflects brain and skull growth, most informative in the first two years.
This calculator is for reference only and does not replace medical advice. It uses the WHO Child Growth Standards for children aged 0–60 months; a single measurement outside the typical range does not by itself indicate a health problem, and a consistent trend across visits matters more than any one data point. Consult a pediatrician or health worker for any concern about a child's growth.
Sources: WHO Child Growth Standards