What a corrected age calculator does
A corrected age calculator works out how old a premature baby is counting from their original due date rather than their birth date. It is also called an adjusted age calculator, and the two terms mean the same thing.
Enter the birth date and either the due date or how many weeks early the baby arrived, and the tool returns the corrected age in weeks and months, the actual age for comparison, and how early the baby was born.
Why corrected age matters
A baby born two months early has had two fewer months to grow and develop than a baby born on their due date. If you compare that baby against full-term babies of the same actual age, they will always seem behind — not because anything is wrong, but because they are effectively younger in developmental terms.
Corrected age fixes that. By counting from the due date, it compares a premature baby against where a baby of the same developmental age would be. This is why corrected age is used for tracking growth, feeding, sleep, and developmental milestones in the early years.
How to calculate corrected age
The method is straightforward subtraction:
Step 1 — Find the actual age
Count the time from the birth date to today. That is the chronological, or actual, age.
Step 2 — Find the weeks of prematurity
Full term is counted as 40 weeks. A baby born at 32 weeks was 8 weeks early. If you know the due date instead, the weeks of prematurity is simply the gap between the birth date and the due date.
Step 3 — Subtract
Take the weeks of prematurity away from the actual age. What remains is the corrected age. A baby who is 6 months old but was born 2 months early has a corrected age of about 4 months.
The calculator above does all of this for you, and also handles the period before the due date has passed, when the corrected age is counted in weeks until term.
How long do you use corrected age?
Corrected age is most useful in the first couple of years, while the head start a full-term baby has still makes a visible difference. Pediatric guidance commonly applies it when assessing growth and milestones until around two years old, after which most children have caught up enough that actual age is used. Your pediatrician may adjust this timeline based on how early your baby was born.
Actual age vs. corrected age
Both numbers are useful, and the calculator shows both. Actual age is what you would use for things tied to the calendar — vaccination schedules are generally given by actual age, for example. Corrected age is what you would use when looking at development, so that progress is measured fairly.
A note on medical guidance
This calculator and page provide general information to help you understand corrected age. They are not a substitute for medical advice. Your pediatrician, neonatologist, or care team knows your baby’s history and is the right source for any decisions about health, development, or milestones.
frequently asked questions
What is the difference between corrected age and adjusted age?
There is no difference — they are two names for the same thing. Both mean a premature baby’s age counted from the original due date rather than the birth date.
How do I calculate my baby’s corrected age?
Take the actual age (from birth to today) and subtract the number of weeks the baby was born early. For example, a baby who is 6 months old and was born 2 months early has a corrected age of about 4 months. Enter the dates above and the calculator does it for you.
What counts as full term for this calculation?
Full term is counted as 40 weeks. A baby born at 34 weeks, for instance, was 6 weeks early, and that 6 weeks is what gets subtracted from the actual age.
How long should I use corrected age?
It is generally used through the first couple of years, with pediatric guidance commonly applying it until around age two. After that most children have caught up and actual age is used. Your care team may suggest a different point depending on how early your baby arrived.
Should I use actual age or corrected age for milestones?
Use corrected age for development and milestones, so your baby is compared fairly against where a baby of the same developmental age would be. Actual age is generally used for calendar-based things like vaccination timing.
Is corrected age the same as gestational age?
No. Gestational age describes how far along a pregnancy was at birth, measured in weeks. Corrected age uses that information after birth to adjust the baby’s ongoing age relative to their due date.