Baby Weight Percentile Calculator
The Baby Weight Percentile Calculator shows where your baby's weight ranks against other children of the same age and sex. Enter the age, sex, and weight, and it estimates the percentile using WHO weight-for-age references, plus the median weight for that age. A percentile of 50 is average; very low or very high values are worth discussing with your pediatrician.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
- Approximate estimate using WHO medians. Your pediatrician uses full LMS charts for precise percentiles.
Formula
z = (weight − median) ÷ SD; percentile from the normal distribution (WHO reference).
- Baby Weight Percentile Calculator gives you a fast estimate using your inputs and updates instantly when you change any value.
- Formula: z = (weight − median) ÷ SD, then convert z to a percentile using the standard normal distribution.
- Input definitions: • Gender: boy or girl, since growth references differ by sex. • Age: the baby's age in months (0–60). • Weight: the baby's weight in kilograms.
- Medians come from WHO weight-for-age references and are interpolated between the charted ages.
- This is a screening estimate using approximate standard deviations — clinicians use full LMS charts for precise percentiles.
- The trend across visits matters more than a single percentile; babies usually track a consistent curve.
Example Calculation
Inputs
- Gender: boy
- Age: 6 months
- Weight: 7.9 kg
A 6-month-old boy weighing 7.9 kg sits right at the WHO median weight for his age, so the estimated percentile is about the 50th — an average weight.
Frequently asked questions
What does a weight percentile mean?
It tells you how your baby's weight compares with other babies of the same age and sex. The 50th percentile is average; the 25th means lighter than 75% of peers.
What percentile is normal?
Roughly the 3rd to 97th percentile is considered typical. Where your baby tracks consistently matters more than the exact figure.
Should I worry about a low percentile?
Not on its own. Many healthy babies are naturally lighter. A sudden drop across percentile lines is what usually prompts a closer look.
My baby is on a high percentile — is that a problem?
Usually not by itself. Your pediatrician considers weight alongside length and head growth to see the full picture.
How is weight measured for this?
Use a recent weight in kilograms, ideally measured on the same scale (without clothes or diaper for young babies) for consistency.
How accurate is this estimate?
It uses WHO medians with approximate standard deviations, so it's a screening estimate. Clinicians use detailed LMS charts for exact percentiles.
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