Corrected Age Calculator for Premature Babies — Months and Weeks

Take your baby’s actual age in weeks and subtract the weeks they were born early, which is 40 minus the gestational age at birth. The AAP’s example: a baby born at 32 weeks is 8 weeks early; at 4 months (16 weeks) old, the corrected age is 8 weeks, about 2 months, so you can expect the developmental skills of a 2-month-old born at term.

Chronological age is the time since birth. Corrected age is chronological age minus the weeks born early, so it counts from the due date. Postmenstrual age is gestational age at birth plus chronological age; this calculator shows it before the due date, when corrected age has not started yet. The AAP Committee on Fetus and Newborn (Engle, 2004) defined these terms to standardise how they are used.

The AAP says that during the first 2 years, using your baby’s corrected age gives a better idea of when they should reach common developmental goals. That is why this calculator points out when your baby has passed their second birthday in chronological age. How to handle it after that point for your own child is a question for your paediatrician.

No. The AAP Committee on Infectious Diseases (2003) states that medically stable preterm infants should receive full doses of the routine vaccines at the chronological age recommended for babies born at term. A baby born 8 weeks early therefore gets the 2-month vaccines 2 months after birth, not at 2 months of corrected age. Corrected age is for following development, not the vaccine schedule.

Yes. The AAP policy statement on age terminology (Engle, 2004) lists adjusted age as a synonym of corrected age: chronological age reduced by the number of weeks born before 40 weeks of gestation. Both names describe the same figure, so this calculator works whichever term your hospital or paediatrician uses.