WHO GROWTH STANDARDS · BIRTH TO UNDER 2
Infant percentile calculator
Compare an infant’s weight, lying-down length and head circumference with the WHO reference for the same exact age and sex. The calculator uses daily reference parameters rather than rounding every baby to a completed month.
Calculate infant percentiles ↗WHO data, recommended by CDC
For children from birth to under age two, CDC recommends the WHO Child Growth Standards. On the second birthday, this site switches to the CDC 2000 child growth reference and standing height.
What the result means
A percentile is a position in a reference distribution, not a percentage of ideal growth. The 42nd weight-for-age percentile means the measurement is larger than about 42% of the reference group at the same age and sex.
What to enter
- Birth date and the exact measurement date.
- Sex used for the growth chart.
- Weight, lying-down length, or head circumference. Only one measurement is required.
One point versus a trajectory
A single percentile describes size on one date. Saving several consistently measured observations can show whether the pattern is broadly steady or changing. The chart’s dotted continuation shows the future WHO values at the latest percentile; it is a reference line, not a prediction of the child’s future size.
Important limits
This tool does not correct age for premature birth, diagnose a condition or interpret feeding, development or family history. Ask a qualified healthcare professional about an unexpected measurement or pattern.
Useful next steps
Sources: CDC recommended growth charts · WHO Child Growth Standards · Calculation methodology.
WORKED EXAMPLE
A fuller six-month snapshot
A girl measured at 185 days, 7.3 kg and 65.7 cm can receive weight-for-age, length-for-age and weight-for-length results from the same visit. The three values answer different questions; none is a diagnosis.
Choose the comparison you need
| Result | Inputs | Adds |
|---|---|---|
| Weight-for-age | Age, sex, weight | Size compared at the same age. |
| Length-for-age | Age, sex, lying-down length | Length compared at the same age. |
| Weight-for-length | Sex, weight, lying-down length | Weight relative to body length. |
Measurement checklist
- Use a baby scale and a recumbent length board when possible.
- Record measurements from the same visit with their original date.
- Repeat a result that seems inconsistent before interpreting it.
Read the weight-for-length guide and worked example.
Questions parents ask
Which infant percentiles can I calculate?
Weight-for-age, length-for-age and head-circumference-for-age can be calculated separately. Enter both weight and length to also see weight-for-length.
Why use exact dates instead of completed months?
Growth changes quickly in infancy. Exact birth and measurement dates select the daily WHO reference rather than treating every infant in a month as the same age.
Can a percentile tell me whether growth is healthy?
No. It describes position in a reference distribution. Interpretation needs the measurement pattern, history and professional context.
Review status: Maintained by Baby Growth and technically reviewed on 29 September 2026. Calculations and product ranges are checked against the cited WHO, CDC and manufacturer sources. This independent tool has not received clinical review and does not replace professional care.