Chronological and corrected age
A baby born early can have two useful age descriptions. Keep both visible and keep their starting dates clear.
Two ages. Clear starting points.
Two starting dates
Chronological age is elapsed time since birth. Corrected age uses the expected due date as its starting point. Neither result changes the baby’s date of birth.
AAP parent guidance describes correcting age for prematurity. The linked guidance is context, not an individual assessment or a review of this website.
How the 40-week reference works
When you enter gestational age at birth, the calculator subtracts completed weeks plus extra days from 280 days. That interval is added to the birth date to obtain a reference due date.
Forty weeks is a calculation reference here. It is not presented as the only medical definition of a full-term pregnancy. The early-birth input accepts 20 weeks through 36 weeks and 6 days; this range is an input boundary, not a diagnosis.
Keep the extra days
At 32 weeks exactly, the difference from 40 weeks is 56 days. At 32 weeks and 3 days, it is 53 days. After 112 days since birth, the corrected results are respectively 56 days (8 weeks) and 59 days (8 weeks and 3 days).
Before the due date, the calculator displays the days remaining until that date. It does not show a negative corrected age or replace the chronological result.
What this comparison cannot tell you
The calculation does not assess developmental delay, assign a score or predict a skill date. It does not decide how long an individual child should use age correction. Ask the child’s healthcare professional which age to use for their care.
Why might a due date and entered gestation give different results?
The due-date method uses the original expected date you enter. The gestation method derives a reference due date by adding 280 minus the entered gestational days to the birth date. Different starting information can therefore produce different reference dates.
Keep the original dates and any extra gestational days. Check uncertain pregnancy information with the care team rather than rounding the inputs until the results match. Both methods continue to show chronological age unchanged.