Corrected age calculator for premature babies
Work out a premature baby’s corrected (adjusted) age — their age counted from the due date instead of the birth date — alongside their actual age. Everything is calculated in your browser; nothing is saved or sent.
Defaults to today.
The due date from the pregnancy.
How to use it
- Enter your baby’s date of birth. Leave “Calculate age on” as today, or change it to check a past or future date — a clinic appointment, for example.
- Add how early your baby arrived. Either the gestational age at birth from the hospital notes (for example 32 weeks 4 days), or switch to Original due date and enter that instead.
- Read both ages. You’ll see the actual (chronological) age, how many weeks early your baby was, and the corrected age to use when checking milestones.
What corrected age means
A baby born eight weeks early has had eight fewer weeks of development in the womb. So when they are four months old by the calendar, it’s fairer to compare their development with a two-month-old’s. That adjusted figure is their corrected age (also called adjusted age). Their age from the actual birth date is their chronological age. Both are “true” — they just answer different questions.
The formula, with an example
Corrected age = chronological age − weeks born early, where weeks early = 40 − gestational age at birth. This is the method the American Academy of Pediatrics describes: a baby born at 32 weeks was 8 weeks (2 months) early, so at 16 weeks old (about 4 months) their corrected age is 8 weeks (about 2 months). Counting from the original due date to today gives exactly the same result, which is why the calculator accepts either.
When to use corrected age — and when not to
Use corrected age when you look at developmental milestones (smiling, sitting, crawling, first words) and when reading growth charts, typically for the first two years. Use chronological age for the vaccination schedule, which normally runs from the birth date. If your baby was very premature or had a long stay in neonatal care, their team may give you specific guidance; follow that over any general rule.
Born early because of twins?
Many twins arrive before 37 weeks, so corrected age often applies to them. If you’re still pregnant with twins, the twin due date calculator shows the usual planned delivery windows. For how term and preterm are defined, see pregnancy trimesters and milestones.
Frequently asked questions
How do you calculate corrected age?
Subtract the number of weeks your baby was born early from their actual age. Weeks early is 40 minus the gestational age at birth. A baby born at 32 weeks was 8 weeks early, so at 16 weeks old their corrected age is 8 weeks (about 2 months). Counting from the original due date gives the same answer.
Is adjusted age the same as corrected age?
Yes. Adjusted age and corrected age mean the same thing: a premature baby’s age counted from their due date instead of their birth date. Chronological age is the age counted from the actual birth date.
Until what age should I use corrected age?
The American Academy of Pediatrics says corrected age gives a better idea of when to expect developmental milestones during the first two years. After that, most children have caught up and their chronological age is used. Your baby’s care team may advise differently for very premature babies.
Do I use corrected age for vaccinations?
No. Routine vaccinations are usually given by chronological age — the age from the actual birth date — not corrected age. Corrected age is mainly for developmental milestones and growth. Follow your baby’s vaccination schedule from their clinician.
Does a baby born at 37 weeks or later need a corrected age?
Usually not. Babies born from 37 weeks are full term or early term, and the small difference from 40 weeks isn’t normally corrected for. The calculator still shows the figure, but flags that correction isn’t usually needed.
Sources
Last meaningfully updated: 2026-10-14.