What is adjusted age?
Adjusted age (also called corrected age or corrected gestational age) is the age a premature baby would be if they had been born at 40 weeks gestation. It is calculated by subtracting the number of weeks premature from the baby's chronological (birth certificate) age.
Formula: Adjusted Age = Chronological Age − Weeks Premature (expressed as a fraction of a year)
The American Academy of Pediatrics (AAP) recommends using adjusted age when tracking developmental milestones for premature infants, and continuing to use it until approximately 2–3 years of age, when most milestone gaps close.
Worked example
1
Baby born at 30 weeks (10 weeks premature). Chronological age today: 6 months.
2
Weeks premature = 40 − 30 = 10 weeks = approximately 2.5 months.
3
Adjusted age = 6 months − 2.5 months = 3.5 months.
4
Use 3.5-month milestones (e.g. holding head up, beginning to smile) — not 6-month milestones.
Prematurity categories
| Category | Gestational Age | Weeks Premature | Use Adjusted Age Until |
|---|---|---|---|
| Late Preterm | 34–36 weeks | 4–6 weeks | ~12–18 months |
| Moderately Preterm | 32–33 weeks | 7–8 weeks | ~2 years |
| Very Preterm | 28–31 weeks | 9–12 weeks | ~2–3 years |
| Extremely Preterm | <28 weeks | 13+ weeks | Up to 3 years |
FAQ
Most developmental paediatricians and the AAP recommend using adjusted age until 2 years old for moderately premature babies, and until 3 years old for very/extremely premature infants. By this age, most children who were premature have caught up developmentally with their term peers. Your child's specific developmental trajectory should be assessed by your paediatrician.
Yes. The CDC and WHO growth charts should be plotted using adjusted age for premature infants until 2–3 years of age. Plotting a premature baby's weight or length against their chronological age will make them appear small or underweight when they may actually be following a normal growth trajectory for their developmental age. Your paediatrician or health visitor will typically do this automatically.
Sources
- American Academy of Pediatrics (AAP). "Age Terminology During the Perinatal Period." Pediatrics. 2004;114(5):1362–1364.
- Engle WA, et al. "Late-Preterm Infants: A Population at Risk." Pediatrics. 2007;120(6):1390–1401.