Baby Percentile Calculator
WHO weight-for-age percentile & z-score for babies 0–24 months. Enter age, weight and sex — get the percentile, z-score and growth category, computed with the official WHO LMS method.
Calculate weight percentile
Uses the WHO Child Growth Standards (2006), weight-for-age daily LMS tables.
Growth curve
Your baby's weight plotted against the WHO 3rd, 15th, 50th, 85th and 97th percentile curves.
WHO LMS reference table
Monthly summary of the official WHO daily LMS tables (weight-for-age). The calculator itself uses the exact daily row.
Boys — L, M, S by month
Girls — L, M, S by month
Worked examples
Computed live by the same engine as the calculator above.
Frequently asked questions
What is a baby weight percentile?
A percentile tells you how your baby's weight compares to the WHO reference population of healthy babies of the same age and sex. The 50th percentile is the median — half of the reference babies weigh less and half weigh more. It is not a score: a healthy baby can sit at the 10th or the 90th percentile.
How is the z-score calculated?
With the WHO LMS method: z = ((weight / M)^L − 1) / (L × S), where L, M and S are the official WHO parameters for your baby's exact age in days and sex. The percentile is the standard normal cumulative distribution of the z-score, times 100.
Which growth standard does this calculator use?
The WHO Child Growth Standards (2006), weight-for-age, using the official WHO daily LMS tables for ages 0–730 days. Your baby's age is converted to days and the exact WHO table row is used — no interpolation.
What do the result categories mean?
Below the 3rd percentile may indicate underweight, the 3rd–97th percentile range is typical, and above the 97th percentile may indicate overweight. These are statistical flags, not diagnoses — only a pediatrician can interpret your baby's growth.
My baby dropped percentiles since last month. Should I worry?
One measurement matters less than the trend over time. Pediatricians look at the growth curve across visits. If the percentile keeps falling, or sits below the 3rd or above the 97th percentile, discuss it with your pediatrician.
Can I use this calculator for a premature baby?
For preterm infants, doctors usually use corrected age (age counted from the due date) until 24 months. This calculator does not adjust for prematurity — ask your pediatrician which age to enter.
Which units can I enter?
Age in months (0–24) plus extra days, converted to total days for the WHO table lookup. Weight in kilograms or pounds — pounds are converted to kilograms before the calculation.
Is my baby's data sent anywhere?
No. The calculation runs entirely in your browser. Nothing is uploaded, stored or shared.
Scope boundary
What this tool does: weight-for-age percentile and z-score for babies 0–24 months, per the WHO Child Growth Standards (2006). What it does not do: length/height-for-age, weight-for-length, BMI-for-age, or ages above 24 months. For a different question — how much formula a baby needs per day — see our baby formula feeding calculator.
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