Corrected age calculator.
For babies born early. Enter the birth date and the original due date to see your baby's actual age, their corrected age and how many weeks early they arrived.
This tool is educational and does not replace your midwife or doctor. Nothing you enter leaves your device.
How corrected age is worked out
Corrected age = actual age − the time between birth and the due date. A baby born 10 weeks early who is now 26 weeks old has a corrected age of 16 weeks. That is the age to keep in mind when you read about milestones.
For babies born prematurely, developmental age is calculated from the original due date, not the birth date, until they are 2 years old.
That is the NHS wording, from its guidance on health and development reviews.
When to use which age
| For | Use |
|---|---|
| Development and milestones | Corrected age, until 2 years |
| Birthdays and legal age | Actual age |
| Vaccinations, weaning, medicines | Ask your health visitor or paediatrician |
See also the baby sleep calculator.
Questions, answered
What is corrected age?
Corrected age, also called adjusted age, is your baby's age counted from the original due date instead of the birth date. A baby born 8 weeks early who is 20 weeks old has a corrected age of 12 weeks.
How long do you use corrected age?
The NHS says that for babies born prematurely, developmental age is calculated from the original due date, not the birth date, until they are 2 years old.
What is corrected age used for?
Development: when to expect smiling, rolling, sitting and so on, and how growth is plotted. Your health visitor or paediatrician will tell you which age to use for anything else, including vaccinations and starting solid foods.
What counts as premature?
A baby born before 37 weeks of pregnancy. ACOG defines term as beginning at 37 weeks 0 days.
Is corrected age the same as adjusted age?
Yes. The two terms mean the same thing.
Sources
- NHS: Your baby's health and development reviews
- ACOG Committee Opinion 579: Definition of Term Pregnancy
Sources last checked on 11 November 2026.