If your baby was born before their due date, you will probably hear your pediatrician talk about corrected age, also called adjusted age. Corrected age is your baby’s age counted from their original due date instead of their actual birth date. It gives a fairer picture of growth and development for premature babies, because a baby born 8 weeks early has had 8 fewer weeks to grow. Pediatricians usually use corrected age for growth charts, milestones and development checks until about age 2. Enter your baby’s date of birth and their original due date below to see both ages side by side.
Corrected Age Calculator
How corrected age is calculated
The formula is simple: corrected age = chronological age − the number of weeks your baby was born early. A baby is considered to be born early when they arrive before their due date, which is based on a full-term pregnancy of about 40 weeks. Worked example: a baby born 8 weeks early is now 6 months old chronologically. Subtract the 8 weeks they were born early (roughly 2 months) and their corrected age is about 4 months. That 4-month figure — not 6 months — is the fair comparison for growth charts and milestones, because it matches the age the baby would be if they had been born on their due date.
Corrected age and growth percentiles
Growth percentiles for premature babies are usually plotted using corrected age, not chronological age. Plotting a preemie against their uncorrected age can make them look smaller than they really are, because it compares them with babies who had extra weeks to grow before birth. When you use our Baby Percentile Calculator, enter your baby's corrected age in months for a fairer result. You can also work out their everyday age with the main Baby Age Calculator and follow growth over time on our Baby Growth Chart page.
Frequently asked questions
What is corrected age?
Corrected age, also called adjusted age, is a premature baby age counted from their original due date instead of their actual birth date. It is calculated by subtracting the number of weeks a baby was born early from their chronological age, and it gives a fairer measure of growth and development.
How long is corrected age used?
Corrected age is usually used until about 2 years of age. By then most premature babies have largely caught up with babies born at term, so doctors gradually stop adjusting and use chronological age. Some clinics correct for up to 2 to 3 years for growth checks.
Should I use corrected age for milestones?
Yes. Pediatricians generally compare a premature baby milestones, such as rolling, sitting and first words, with their corrected age rather than their chronological age, usually until around age 2. This avoids expecting a baby born early to reach milestones before they are developmentally ready.
What if my baby was born at 36 weeks?
A baby born at 36 weeks arrived about 4 weeks before their 40-week due date, so you subtract 4 weeks from their chronological age. For example, a baby who is 12 weeks old chronologically and was born at 36 weeks has a corrected age of about 8 weeks.
Disclaimer: This calculator is for general information only and is not medical advice. Premature babies can have individual health needs, so always follow your pediatrician's guidance about growth, feeding and development.