Preemie Corrected Age Calculator (Adjusted Age)

What corrected age means

Corrected age — also called adjusted age — is the age your baby would be if they had been born on their due date. A baby born 8 weeks early who is 16 weeks old has a corrected age of 8 weeks. That’s the age to keep in mind when you think about what your baby is ready to do.

You’ll hear a few different “ages” in the NICU and afterward:

• Chronological age is the time since your baby was born — their age by the calendar.
• Gestational age is how far along the pregnancy was when your baby was born. A full-term pregnancy is about 40 weeks, so a baby born 10 weeks early has a gestational age of 30 weeks.
• Postmenstrual age is gestational age plus chronological age. A baby born at 30 weeks who is now 8 weeks old has a postmenstrual age of 38 weeks. You may hear it while your baby is still in the NICU, before their due date.
• Corrected age is chronological age minus the weeks your baby was born early.

The American Academy of Pediatrics published standard definitions for these terms so doctors and researchers describe babies’ ages the same way. For more NICU vocabulary, see our NICU glossary.

How to calculate corrected age by hand

The American Academy of Pediatrics describes it in two steps:

• Find how many weeks early your baby was born. Subtract your baby’s gestational age at birth from 40 weeks. A baby born at 32 weeks was born 8 weeks early.
• Subtract that from your baby’s actual age. If that baby is now 16 weeks (about 4 months) old, 16 − 8 = 8 weeks. Her corrected age is about 2 months.

If you know your due date, there’s an even simpler way: corrected age is just the time since your baby’s due date. That’s what the calculator above does.

If your baby hasn’t reached their due date yet, there’s no corrected age to count up — it’s still “before the due date.” The calculator shows how many weeks remain and the postmenstrual age instead.

When to use corrected age

Corrected age helps set fair expectations. In the AAP’s example, a 4-month-old born at 32 weeks would be expected to have the developmental skills of a 2-month-old term baby — so it isn’t realistic to expect her to roll over yet. If a relative says your baby seems “behind for a 4-month-old,” corrected age is often the reason.

The AAP says that during the first 2 years, using corrected age gives a better idea of when to expect common developmental milestones. Nationwide Children’s Hospital notes that many babies born early catch up to their full-term peers by age 2, and correcting for prematurity is then no longer needed.

Corrected age is mainly used for babies who were born premature — before 37 weeks. If your baby was born after their due date, or within a few weeks of it, their corrected age and chronological age are the same or nearly so.

Every baby develops at their own pace. If you have questions about your baby’s milestones, ask your pediatrician which age they’re using and why.

Vaccines follow your baby’s actual age

Here’s one place corrected age does not apply. According to the CDC’s immunization best-practice guidelines, in most cases babies born early should get their vaccines at the same chronological age, and on the same schedule, as full-term babies. Birth weight and size aren’t factors in deciding whether to vaccinate a clinically stable preterm baby.

The CDC notes a few special situations your baby’s team will handle:

• Hepatitis B. The timing of the hepatitis B vaccine can be different for some preterm, low-birth-weight babies.
• Rotavirus. For a baby who is at least 6 weeks old and has been in the hospital since birth, the CDC recommends waiting to give rotavirus vaccine until discharge.

Ask your NICU team which vaccines your baby has had before you go home, and bring that record to your first pediatrician visit. RSV protection is its own topic — see RSV after the NICU.

Follow-up after the NICU

In Boise, the St. Luke’s Children’s NICU Follow-up Clinic provides ongoing developmental follow-up for NICU graduates. You’ll find its contact details, along with other local support, on our Treasure Valley NICU resources page.

Getting ready for discharge? Our guide to bringing your NICU baby home covers what usually happens before you leave.