weightforage

Weight-for-age is an anthropometric indicator used in pediatric growth assessment to compare a child's weight with the expected weight for their age, based on reference populations. In practice, it is most commonly expressed as a z-score, known as the weight-for-age z-score (WAZ), and is applied primarily to children from birth up to five years of age.

Calculation and interpretation: The WAZ is calculated by subtracting the reference median weight for the child's age from the observed weight and dividing by the reference standard deviation. Values are typically drawn from the World Health Organization (WHO) Child Growth Standards or national references. A WAZ around zero indicates average weight for age; a WAZ of -2 or lower indicates underweight, with -3 or lower indicating severe underweight. Values above +2 may indicate overweight relative to age, though overweight and obesity are usually assessed with other indices such as weight-for-height or BMI-for-age.

Uses: Weight-for-age is used in clinical care to identify undernutrition in individual children and to monitor growth over time. At the population level, it supports nutritional surveillance, program planning, and evaluation of interventions targeting child malnutrition.

Limitations: Because weight-for-age combines the effects of stunting (low height for age) and wasting (low weight for height), it cannot distinguish chronic from acute undernutrition. It is sensitive to errors in age reporting and weight measurement, and to acute illness and edema. For a fuller assessment, it is interpreted alongside height-for-age and weight-for-height (or BMI-for-age) measures.

See also: related indicators include height-for-age, weight-for-height, BMI-for-age, and mid-upper arm circumference.