What percentiles mean
A percentile compares your baby with a reference population. Being on the 25th percentile means about 25% of babies of the same age and sex weigh less, and 75% weigh more. Anywhere between the 2nd and 98th centile is generally considered normal.
The curve matters more than one number
A baby on the 9th centile who tracks steadily along that line is usually growing well. What health visitors watch for is a marked change — crossing two or more centile lines up or down — which is worth reviewing.
Which chart to use
The WHO growth standard is used for babies (based on breastfed infants growing in healthy conditions); some countries use CDC charts, and specialist charts exist for premature babies and specific conditions. Always use the chart your health team recommends.
When to ask for advice
Speak to your health visitor or GP if your baby’s weight crosses centile lines, if feeding is a struggle, if there are fewer wet nappies than usual, or if you’re simply worried. Early, friendly advice is always better than guessing.