Corrected & Chronological Age

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Jacqueline F. Gould, Belinda G. Fuss, Rachel M. Roberts, Carmel T. Collins, Maria Makrides. 

Children born preterm (gestational age at birth <37 weeks) are at increased risk of experiencing impairment compared to their term born peers. Children born preterm score significantly lower than their full-term peers on tests of cognition and motor skills and are more likely to have neurodevelopmental deficits. The likelihood of a child experiencing poor outcomes increases as gestational age at birth decreases. 

It is routine practice in many developed countries to follow-up and assess the development of children born at the earliest gestations or with a low birth weight in order to facilitate early detection of deficits and assign intervention. Developmental test scores are age standardized according to chronological age (calculated from date of birth) at time of assessment. However, there is debate as to whether corrected age (CA: adjusted for preterm birth, calculated from the estimated date of conception) is more appropriate for children born preterm, and if so, at what age is correction no longer necessary. 


When a baby is born before their due date, they will have two ages: their corrected age and their chronological age. Your baby also had a gestational age, which was the age of your baby from conception to birth, calculated in weeks. 

When following your baby’s growth and development, it can be helpful to know the difference between the ages: 

Corrected age: The age your baby would be if they had been born on their due date. For example, a baby who was born three months early (who now has a chronological age of seven months) has a corrected age of four months. Corrected age is useful while following your baby’s growth and development. 

Chronological age: The age of your baby since birth. Your child's birthdays are celebrations of his or her chronological age. 

For most pre-term babies, you will only need to correct their age until they are two or three years, as by this time most children have caught up developmentally to their peers. 

Why corrected age is important? 

Corrected age can help if you’re trying to work out whether your premature baby’s development is tracking in a typical way. For example, if someone notices that your baby is 6 months old but not sitting up yet, you could explain that your baby was born 3 months early. If you look at your baby’s corrected age, they’re only 3 months old and they’re doing everything a 3-month-old usually does. 

Corrected age is most relevant during your child’s early years because it might explain things that look like delays in development in these years. 

How to calculate your baby’s corrected age 

You can calculate your baby’s corrected age by subtracting how many weeks premature they were born from their actual age (how many weeks since they were born). 

Chronological age minus how many weeks premature = Corrected age 

For example, if you baby’s chronological age is 16 weeks (they were born 16 weeks ago) and they were 8 weeks premature, there corrected age is 8 weeks. 

16 weeks old minus 8 weeks premature = 8 weeks corrected age 

To calculate your baby’s corrected age, see this online calculator. Be sure that you are using the same due date as your health team, so that you calculate the same corrected age. 


All children have variations in growth and development, regardless of whether they were premature or born at term. 

Being premature can affect different areas of growth and development differently. Some areas might not be affected at all, whereas others could be greatly affected. Using your baby’s corrected age for growth is particularly important. 

It’s a good idea to tell your child health nurse at your first visit, your mother’s group, early childhood educators and health professionals and anyone who cares for or works with your child that your child was born prematurely. These people will probably also find it useful to know how many weeks early your child was born. 

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Disclaimer: This publication by Miracle Babies Foundation is intended solely for general education and assistance and it is it is not medical advice or a healthcare recommendation. It should not be used for the purpose of medical diagnosis or treatment for any individual condition. This publication has been developed by our Parent Advisory Team (all who are parents of premature and sick babies) and has been reviewed and approved by a Clinical Advisory Team. This publication is not a substitute for professional medical advice. Miracle Babies Foundation recommends that professional medical advice and services be sought out from a qualified healthcare provider familiar with your personal circumstances.To the extent permitted by law, Miracle Babies Foundation excludes and disclaims any liability of any kind (directly or indirectly arising) to any reader of this publication who acts or does not act in reliance wholly or partly on the content of this general publication. If you would like to provide any feedback on the information please email [email protected].