Weight-for-Age Percentile Calculator (WHO, 0-24 Months)

How Weight-for-Age Percentiles Work

Weight-for-age percentiles compare your child’s weight to the weights of other children of the same age and sex from the WHO Multicentre Growth Reference Study. This study followed healthy breastfed children from six countries to establish universal growth standards.

The calculator uses the LMS method (Lambda-Mu-Sigma), a statistical technique that summarizes the distribution of weight at each age using three parameters. Lambda (L) accounts for the skewness of the distribution, Mu (M) is the median, and Sigma (S) is the coefficient of variation.

Understanding Percentiles

A percentile indicates the percentage of children who weigh less than your child. For example, if your baby is at the 75th percentile, 75% of babies of the same age and sex weigh less.

• 3rd to 97th percentile is considered the normal range
• Below the 3rd percentile may indicate underweight
• Above the 97th percentile may indicate overweight
• The trend over time matters more than a single measurement

Example Calculation

A 6-month-old boy weighing 7.9 kg would be approximately at the 50th percentile (Z-score near 0), since the WHO median weight for boys at 6 months is 7.934 kg.

Frequently Asked Questions

What age range does this calculator cover?

This calculator uses WHO growth standards for children from birth to 24 months (2 years). For older children, WHO provides separate growth references.

Should I use my child’s weight in kg or pounds?

You can use either unit. The calculator converts pounds to kilograms automatically. For the most accurate result, use the weight recorded at your pediatrician’s office.

Is a single percentile reading concerning?

Not necessarily. Pediatricians look at growth trends over multiple visits. A child consistently at the 15th percentile who is growing steadily is usually healthy. Sudden drops or jumps across percentile lines may warrant further evaluation.

Are these the same charts my doctor uses?

The WHO growth standards used here are recommended by the CDC for children under 2 years of age in the United States and are used by health professionals worldwide.