How to calculate your baby’s age and corrected age
Age in weeks and months
Count the days since the birth and divide by 7 for weeks. For months, count the “month birthdays”: a baby born on 10 May is 1 month old on 10 June.
Corrected age, step by step
- Take 40 weeks and subtract the week the baby was born. Born at 32 weeks → 8 weeks early.
- Subtract those weeks from the baby’s age. 16 weeks old − 8 weeks = 8 weeks corrected age.
Try it with the baby age calculator.
When to stop using corrected age
Corrected age helps most during the first 2 years (AAP). Your baby’s doctor will tell you when to use the real age only.
Sources
- HealthyChildren.org (American Academy of Pediatrics): Corrected age for preemies · checked October 26, 2026
- WHO: Preterm birth fact sheet · checked October 26, 2026