# WHO Percentile Calculator: Guide to Understanding Your Baby's Growth
5 key points for interpreting your baby's percentiles
No single percentile defines your baby's health: the growth trend over time is what matters.
Percentiles between P3 and P97 are considered within the statistical normal range.
BMI in babies follows its own curves and should not be compared with adult reference values.
WHO charts are based on babies raised in optimal conditions, including exclusive breastfeeding in the first months.
Always share growth records with your paediatrician for proper clinical interpretation.
# How to measure your baby correctly
- Weigh the baby without clothes and on the same scale whenever possible.
- Measure length lying down (recumbent) until 24 months.
- From 2 years of age, measure height in a standing position.
- Take measurements at the same time of day for greater consistency.
A percentile below P3 does not automatically indicate a health problem. The most important thing is to observe whether the growth curve maintains its trend over time.
# Interpreting percentiles
| Percentile | Interpretation | Recommended action |
|---|---|---|
| P97 or above | High range | Discuss with the paediatrician at the next visit |
| P85 to P97 | High normal | Routine follow-up |
| P15 to P85 | Normal | No special action required |
| P3 to P15 | Low normal | Routine follow-up |
| P3 or below | Low range | Consult the paediatrician |
# WHO vs Orbegozo Charts
WHO Charts
International standard based on babies from 6 countries raised in optimal conditions.
- Validated international standard
- Based on babies from 6 countries in optimal conditions
- Up to date with current scientific support
- May not reflect local genetic variations
Orbegozo Charts
Charts adapted to the Spanish population, widely used in previous decades.
- Adapted to the Spanish population
- Widely used in Spain in previous decades
- Based on older reference population
- Lower international adoption
WHO 0-5 years Reference standard
Growth trend Key variable
LMS parameters Technical precision
- Z-Score
- Number of standard deviations a value is from the mean of the reference population. A Z-Score of 0 is equivalent to the 50th percentile.
- Harmony
- Appropriate proportion between weight and height. A baby may have a low weight percentile but still be harmonious if their height percentile is similarly low.
- Anthropometry
- Set of body measurements (weight, height, head circumference, BMI) used to evaluate growth and nutritional status.
- LMS parameters
- Statistical method (L=Box-Cox, M=median, S=coefficient of variation) used by the WHO to build percentile tables and convert any measurement into a Z-Score.