Adjusted Age Calculator for Premature Babies

Adjusted age (also called corrected age) is calculated from your baby's original due date, not their actual birth date. This gives a more accurate picture of where your premature baby should be developmentally.

Premature babies need extra time to catch up because they missed out on important growth that would have happened in the womb. Using adjusted age helps set realistic expectations and reduces unnecessary worry about milestones.

A baby born January 1, 2026 with a due date of March 1, 2026 was born 8.4 weeks (59 days) early. On June 1, 2026:

• Chronological age: 5 months (from the birth date)
• Corrected age: 3 months (from the due date)
• Formula: corrected age = assessment date − due date

For milestone tracking, this baby is compared against 3-month expectations, not 5-month ones. Correction is typically used until the second birthday — January 1, 2028 in this example.

Preterm babies are described by several different ages, and hospitals switch between them depending on where the baby is in its care. The calculator reports all of them from the same two dates.

Postmenstrual age is the figure a neonatal unit is most likely to quote in the first months — a baby born at 32 weeks who is 3 weeks old is 35 weeks postmenstrual. Corrected age takes over once the baby is home, because it answers the question parents actually have: how does this baby compare to a term baby of the same developmental stage?

Many parents remember “born at 32 weeks” long after the original estimated due date has been forgotten. Switch the calculator to I know the weeks and enter the gestational age at birth instead — the due date is worked back from it, since a due date is by definition 40 weeks 0 days.

The two routes give the same corrected age, so use whichever number you actually have. If you have both and they disagree, the due date recorded in the medical notes is the one to trust.

Adjusted age should be used for:

• Tracking developmental milestones (sitting, crawling, walking)
• Speech and language development expectations
• Growth chart interpretations
• Early intervention assessments
• Comparing development to age-based norms

Important: Always use chronological age (actual birth date) for vaccinations and medication dosages.

Most healthcare providers recommend using adjusted age until your child reaches age 2. By this point, most preterm babies have caught up developmentally with their full-term peers. However, for very premature babies (born before 28 weeks), some providers may continue adjustments a bit longer.