Corrected age for babies born preterm

A baby born before 37 completed weeks has two useful ages for a while. Actual age counts from birth. Corrected age counts from the original due date, giving developmental timing the weeks the baby would otherwise have had before birth.

How the timeline calculates it

1. We calculate actual age from birthday to today.
2. We calculate how many days lay between birthday and expected due date.
3. We treat the expected due date as 40 weeks and subtract the days early to estimate gestational age.
4. Correction is eligible only when that estimate is before 37 completed weeks: at least 22 days before the due date.
5. For eligible babies, we subtract the days early from actual age, never going below zero.

Example: a 16-week-old baby born 6 weeks before their due date has a corrected age of about 10 weeks.

This is a simple date-based estimate. A clinical record of gestational age can be more precise, so ask your baby’s clinician if the dates do not match what you were told.

Where corrected age appears

UK NICE recommendations 1.1.13 and 1.3.7 use corrected age when assessing functional and developmental skills in children born preterm, up to 2 years. This timeline therefore uses corrected age only on reviewed developmental notes where the source and editorial policy allow it. The actual-age marker remains visible for calendar context such as birthdays.

Correction stops on the child’s calendar second birthday, rather than after a fixed number of days. After that point, the timeline shows actual age only.

Where it does not appear

We do not automatically shift crying trends, sleep-change bands or growth measurements. Those topics need their own evidence and clinical context. A professional may use more information than this simple calculation, including gestation, health and growth history.

Not a diagnosis

Corrected age makes broad timing fairer. It cannot decide whether development is on track. If you have a concern, bring it to your child’s clinician or health visitor now rather than waiting for a later point on the timeline.