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Understanding growth charts

Help! My baby isn't following the percentile lines.

What’s normal for breastfed babies? 

group of babies

Growth charts are used to help follow and assess a baby's growth. Your baby's weight can be plotted against a weight-for-age growth chart.

The most common type of growth chart is a percentile chart where these hundreds of weights are then divided into 100 equal groups. These groups are then plotted on a graph or listed in a table. 

The World Health Organization growth standards are based on healthy, exclusively breastfed babies from six countries across five continents. These show how a normal baby grows. There are charts for weight, length and head circumference, each of which should be plotted as the baby grows.  

Older charts were based on a mix of breastfed and formula-fed babies, each with different growth rates. These may still be used in some places, so check that your baby’s growth is being plotted on the WHO charts. (If your baby record book does not contain the WHO growth standards, you may like to print them out and put them in your book.) 

You can find these World Health Organization child growth percentile field tables at: 

Girls weight for age – birth to 6 months 

Boys weight for age - birth to 6 months 

How do I read a growth/ percentile chart?

The growth charts can be difficult to read and understand. Many people misinterpret what they see on the charts.  

It is the pattern of growth over time that is important, not the growth from week to week. 

  • 3% of babies will be below the 3rd percentile and 3% of babies will be above the 97th percentile 

  • 15% of babies will be below the 15th percentile and 15% of babies will be above the 85th percentile 

  • 50% of babies will be below the 50th percentile and 50% of babies will be above the 50th percentile 

Does it matter if my baby doesn't 'stick' to a percentile line? 

Usually, no. Percentile charts are derived from the averaged measurements of hundreds of babies and so they show “smoothed” growth curves, which individual children shouldn't be expected to follow exactly. They can and do grow faster or slower at times.  

A large US study found that: 

  • About ¾ of babies cross weight-for-age percentile lines over the first 6 months.   

  • More than 1/3 of babies move up or down two percentile lines. 

  • From birth to 6 months, larger babies tend to put on weight more slowly (on average) and smaller babies put on weight more quickly.  

  • As children get older, they are less likely to cross two percentile lines, but it does sometimes happen. 

If your baby has continued low weight gains with a pattern of weight gain showing dropping percentiles at a faster rate than expected, it's important to see your doctor.   

Remember, the 50th percentile on the chart is an average, not a 'pass'. It's not something to aim for. It's not something to achieve. It just means that 50% of babies growing normally will be below it and 50% will be above.

If your baby is ‘low’ on the charts, they aren't failing and it usually isn't a problem. 

© Australian Breastfeeding Association April 2022