A weight percentile compares your baby’s weight with children of the same age and sex. It is not a percentage score for health. Changes over time, reliable measurements and a medical check matter more than one number.
A percentile is a position, not a target
- Below
- ≈ 25 out of 100Children who weigh less
- Position
- 25th percentileNot a health percentage
- Above
- ≈ 75 out of 100Children who weigh more
What the number means
The 25th percentile means about 25 out of 100 children in the comparison group weigh less and 75 weigh more. It does not mean your baby is “only 25 percent healthy”. The 50th percentile is the middle, not a target weight for every baby.
Check which chart you are reading
Some WHO charts compare weight with age, while others compare weight with length. Check which chart you are looking at and which units it uses. Only compare matching measurements. Premature babies may need their results interpreted differently.
One point does not describe the pattern
Your baby’s weight changes over time. Do not change feeding because of one measurement alone. Different scales or measuring conditions can give different results. Discuss clear changes in the curve with your baby’s doctor.
For an appointment, a simple list helps: date, measurement, unit and where it was measured. Copy the value as recorded rather than rounding it towards an expected line.
Sources: NHS
Questions to bring to an appointment
At your appointment, ask: are we using the right chart for my baby? Does this change matter? When should we measure again? These questions help more than frequent weighing without a clear reason.
Our illustration explains percentiles using 100 made-up points. It is not a real growth chart and gives no weights in kilograms to compare your baby with.
When to seek support
Ask your baby’s clinician about unexpected weight changes, poor feeding or growth concerns. Do not wait to interpret a chart before seeking help for an acutely unwell baby.
Common questions
Is the 50th percentile best?
No. It is the middle of the comparison group. Your baby does not need to reach it.
Are the illustration’s points actual WHO data?
No. They explain the ranking principle. Original charts are linked in the sources.
Sources & further information
The sources for this guide are linked below. Examples and everyday tips help explain the topic; they are not a personal plan for your baby. Sources last accessed on 20 September 2026.
- WHO: Child Growth Standards — Weight-for-age
World Health Organization reference data.
- NHS: Your baby’s weight and height
UK public-health guidance.
- NHS: Dehydration
UK public-health guidance.
This guide was created with AI assistance and has not been medically reviewed. How we create our guides.
