How to Calculate the Age of Your Premature Baby: Adjusted (Corrected) Age

Babies who are born before 37 weeks gestation are referred to as being born preterm or premature.

In 2013, The American College of Obstetricians and Gynecologists recommended that babies not be considered Full Term until 39 weeks.

Since the 1930s, doctors have given preterm babies two ages: a chronological age and an adjusted or corrected age.

  • The chronological age of a premature baby is the age of the baby from the date of birth.
  • The adjusted or corrected age of the premature baby is the age of the baby based on the due date.

For example, if a baby’s chronological age is 3 months, but he or she was born one month early, the baby is said to have an adjusted age of 2 months.

Adjusted Age = (Chronological Age) – (Number of Weeks or Months Premature)

baby foot in the NICU

It is important to know a baby’s adjusted age, especially when it comes to developmental milestones. The adjusted age signifies that the baby was born prematurely, and therefore his or her brain and neurological system will not be as developed as a baby who was born at term. Thus, the premature baby will not reach developmental milestones at the same time as a term baby would, meaning he or she will likely sit up unassisted later, begin to crawl later, and more. Note: It’s important to talk to your child’s doctor about missed milestones or developmental concerns whether or not your baby was born prematurely.

Babies born prematurely will be monitored more closely in clinical settings, because prematurity is considered a notable risk factor in a child’s development. Medical professionals will usually ask for both chronological age and adjusted age at these appointments as part of the physical examination.

Some studies have shown that age adjustment is more important for motor skills than for cognitive skills, noting that premature infants tend to score significantly lower on motor skills than on mental skills in the first year of life. For these reasons, it is important to know and discuss both ages of a premature baby with your child’s doctors.

Most healthcare professionals will use a corrected age with a child until he or she reaches between 2 and 3 years of age. They do this because it normally takes premature babies roughly that long to “catch up” to babies who were born at term. In a 1991 study, Ouden and colleagues found that, in the first year of life, 80-99% of premature infants achieved positive scores on age-specific developmental tasks when adjusted ages were used, while only 30-80% achieved positive scores when chronological ages were used. At 2 years of age, more than 90% of these same infants had positive scores on age-specific developmental tasks regardless of whether adjusted age was used. This indicates that usage of the adjusted age before two years would eliminate unnecessary referrals for interventions, but that the adjusted age is no longer as necessary after 2 years of age.

Corrected Age in Premature Infants

Age Number of Weeks Needed to Correct = Number of Weeks of Prematurity x 10

Though physicians vary on its usage, there are new findings that support the corrected age being used based on the number of weeks the baby is premature.

For example, if a child is ten weeks premature, it is estimated to take him or her 100 weeks to “catch up” to other babies his or her age.

Featured Videos

Testimonial from Keziah’s Family

Posterior Position

Hypoxic-Ischemic Encephalopathy (HIE)

quotation mark

Featured Testimonial

What Our
Clients Say…

After the traumatic birth of my son, I was left confused, afraid, and seeking answers. We needed someone we could trust and depend on. ABC Law Centers was just that.

- Michael

Helpful resources