GROWTH GUIDE · BIRTH TO 24 MONTHS
Infant and baby weight percentile calculator
Weight-for-age compares a baby’s weight with the WHO reference for the same age and sex. It does not take their length into account.
Calculate weight percentile ↗Take a consistent measurement
Use a baby scale on a stable, level surface. Record the measurement and date as accurately as possible, and keep clothing and weighing conditions consistent between visits.
Understand the number
The 50th percentile is the middle of the reference distribution. A baby near the 25th percentile has a larger measurement than approximately 25% of the reference group at that age and sex. A percentile is not a percentage of ideal growth.
A weight percentile alone cannot tell you whether a baby is underweight or overweight. Length, feeding, medical history and the pattern over time also matter.
Reference values by age
Reference, not diagnosis
Talk to your healthcare professional about a measurement or trend that concerns you. This tool does not correct age for babies born prematurely.
Source: WHO weight-for-age tables. Read the calculation methodology.
WORKED EXAMPLE
Why 7.3 kg can produce two useful results
For a girl at 185 days, 7.3 kg gives a weight-for-age comparison. Add a 65.7 cm recumbent length and the calculator also reports weight-for-length, which adds body-proportion context.
Weight-for-age or weight-for-length?
| Comparison | Uses | Best read as |
|---|---|---|
| Weight-for-age | Exact age, sex and weight | Weight relative to same-age children. |
| Weight-for-length | Sex, weight and recumbent length | Weight relative to same-length infants. |
| Saved trajectory | Several dated measurements | Change over time, with professional context. |
Calculate and understand weight-for-length.
Questions parents ask
Does weight percentile account for length?
No. Weight-for-age uses age and sex. Enter length as well to calculate weight-for-length.
Is the 50th percentile a target?
No. It is the median of the reference distribution, not an ideal that every child should approach.
Why can a percentile change?
Real growth, measurement variation, age precision and the reference used can all affect the displayed position.
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.