Chronological Versus Corrected Age

How to calculate your baby's actual age versus adjusted age

If your baby was born prematurely, there are two important dates to remember. The day your baby was born is the official date of birth, but your original due date is also a very important milestone for your baby.

Your Baby's Actual (Chronological) Age:

Actual age, or chronological age, is your baby's real age, calculated from your baby's actual birthday. Adjusted age, or corrected age, is calculated from when your baby was due.

(Your pregnancy due date.)

Full-term gestation in the womb is considered 38-40 weeks, and babies born within this timeframe are considered "term." Babies that are born before 38 weeks gestation are considered "preterm." Adjusted age takes into account the weeks of pregnancy that were missed when a baby is born prematurely.

Example: A baby born at 25 weeks gestation who is now 16 weeks old by actual age is 1 week old by adjusted age. This baby who is four months old (actual) is not expected to have met the same developmental milestones as a four-month-old who was born at term. Instead, this baby will be more on track with a baby who is just one week old. This is where you would adjust your baby's age. Actual age=4 months. Adjusted age=1 week.

Why is it so important for me to calculate and remember my baby's corrected age?

Your baby's brain grows and develops in two main ways: first according to a pre-programmed biological sequence and second based on the response to their environment and experiences.

Example: A baby will learn to walk when they are developmentally ready. You cannot change or "hurry up" this process simply by practicing the experience. This is a pre-programmed developmental sequence. You may hold your child's hand, and with guidance and help with push toys, you may be able to practice, but until your child is developmentally ready to do so, they will not take their first steps.

This is the same with a baby in the NICU that is "learning and practicing" feeding. We can certainly guide them in the process, but until they are developmentally ready to do so, they will be unable to finish their feedings completely. 

Corrected age can be helpful as a guide to determine if your premature baby’s development is on track based on their adjusted age.

Example: Your baby was born 8 weeks early at 32 weeks gestation, and your baby is now one-year-old actual. Your baby's adjusted age would be 10 months old. You should be following a developmental guideline for your baby based on your baby's age of 10 months old and not one year of age.

In what circumstance is corrected or adjusted age not used?

Immunizations are typically kept on track with a baby's actual age and not their adjusted age. Immunizations protect your preemie against community and environmental diseases that can be spread from person to person. It is best to speak to and make a plan with your baby's pediatrician about vaccinations and the proper schedule for you child and their needs.

A quick reference to calculate your baby's adjusted age:

  • Chronological or actual age: __________
  • The number of weeks your baby was premature: _________
  • Subtract the number of weeks premature from the chronological/actual age =  Your baby's adjusted age: ______________
  • Divide your baby's adjusted age in weeks by 4 to determine your baby's adjusted age in months: ______________

Knowing your premature baby's two ages and keeping track of your baby's adjusted age will help you and your doctor track your preemie's development and be proactive with early interventions if needed.

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