Corrected age calculator for premature babies

Born early? Her age since birth and her age for milestones are two different numbers. Get both, in months, weeks and days.

Short answer: Corrected age (also called adjusted age) is your baby's age minus the weeks she was born early, which is 40 minus her weeks of pregnancy at birth. It is the same as counting from her due date. A baby born at 32 weeks is 8 weeks early, so at 4 months old her corrected age is 2 months. Pediatricians use it for milestones until about age 2.

Nothing you enter is stored or sent anywhere. The calculator counts exact calendar months and days from her due date, which gives the same result as subtracting the weeks she was born early.

How long to use it, and when to ask

The American Academy of Pediatrics recommends using corrected age to track development during the first two years. By age 2, most children born early have caught up to the typical milestone range; if a child hasn't, she may need extra support for longer. Babies born at 37 weeks or later count as full term (the CDC defines preterm birth as before 37 completed weeks), so the adjustment is small.

Corrected age only adjusts for being born early; it can't account for her health or a stay in the NICU, and it isn't a screening. If a skill you'd expect by her corrected age hasn't appeared over a stretch of months, if she loses something she could do before, or if something has quietly worried you for a while, talk to your pediatrician.

In the Introduction to Big Bang Baby I tell the story of Ana María, whose son Joaquín was born at 32 weeks. She reshaped activities built for a general developmental path around Joaquín and did them with him every single day: meeting her child where he actually was. Read the Introduction free. Why the sequence matters more than the date is the heart of Chapter 4.

Sources

American Academy of Pediatrics, HealthyChildren.org: Corrected Age For Preemies (adapted from Understanding the NICU, AAP, 2017). Definition, the 32-week example and use during the first two years.
American Academy of Pediatrics, HealthyChildren.org: Your Preemie's Growth & Developmental Milestones (AAP, 2019; updated 2024). Adjusted age until age 2; most children caught up by then.
Centers for Disease Control and Prevention: Preterm Birth (before 37 completed weeks of pregnancy). The CDC's Milestone Tracker also uses corrected age for babies born early.
Big Bang Baby, Introduction, "Ana María and Joaquín"; Chapter 4, "Cooling and Differentiation".