What is corrected age?
Corrected age, also called adjusted age, is how old a premature baby would be if they had been born on their due date. It is the baby’s chronological age minus the number of weeks they were born early. A full-term pregnancy is counted as 40 weeks, so a baby born at 30 weeks was born 10 weeks early.
Corrected age matters because development tends to follow the due date more closely than the birth date. A baby born 10 weeks early who is 6 months old by the calendar is, developmentally, closer to a 3½-month-old. Comparing them with 6-month-olds would make them look delayed when they may be right on track.
How to calculate corrected age by hand
- Find how early the baby was born: 40 weeks − gestational age at birth. Born at 30 weeks 0 days → 10 weeks early (70 days).
- Find the due date: birth date + the days early. Born January 1, 2025 + 70 days → due March 12, 2025.
- Count the age from the due date to the test date, the same way you would count chronological age.
| Value | |
|---|---|
| Date of birth | Jan 1, 2025 |
| Gestational age at birth | 30 weeks 0 days |
| Born early by | 10 weeks (70 days) |
| Due date | Mar 12, 2025 |
| Test date | Jul 12, 2025 |
| Chronological age | 0;6.11 |
| Corrected age | 0;4.0 |
On the test date, the baby is 6 months and 11 days old by the calendar, but 4 months old corrected.
When should you use corrected age?
- Who: babies born before 37 weeks of pregnancy. Babies born at 37 weeks or later are full term and don’t need correction.
- Until when: correction is most often used until about age 2, and sometimes until age 3 for babies born very early. After that, most children are assessed by chronological age.
- For what: developmental milestones, growth charts and many developmental assessments. Always follow the scoring rules of the specific test you are using.
- Not for vaccines: immunization schedules follow chronological age, not corrected age.