Corrected age calculator
Corrected age adjusts a preterm infant’s chronological age by the time that was missing to complete 40 weeks. It is the age used to assess growth and neurodevelopment in follow-up. Before term, the useful reading is the postmenstrual age.
Enter the gestational age at birth and the date of birth (or days of life). The result shows the postmenstrual age, used until the baby reaches 40 weeks, and the corrected age in weeks and months, used in follow-up until 3 years.
CA = chronological age − (40 weeks − GA at birth). Before term the value is negative on purpose: it is the time left until the newborn reaches 40 weeks. Correct age until 3 years for weight, length, head circumference and neurodevelopment; immunization and the introduction of solids follow chronological age.
Clinical decision-support tool for use by healthcare professionals. It does not replace clinical judgment or your unit's protocols.
Formula
Corrected age = chronological age − (40 weeks − gestational age at birth). Postmenstrual age = gestational age at birth + chronological age. Until the newborn reaches 40 weeks the corrected age is negative on purpose: it is the time left until term.
How long to correct
Correct until 3 years for all parameters: weight, length, head circumference and neurodevelopment. This is the American Academy of Pediatrics recommendation and the upper end of the SBP’s 2-to-3-year range. Immunization and the introduction of solids follow chronological age.
Example
Infant born at 32 weeks, now 5 months of chronological age. 40 − 32 = 8 weeks were missing, about 2 months. Corrected age = 5 − 2 = 3 months. In the calculator: GA 32 weeks and 0 days, 152 days of life. Postmenstrual age 53 weeks and 5 days; corrected age 13 weeks and 5 days, or 3.2 months.
Frequently asked questions
Why does the corrected age show as negative?
Because the baby has not yet reached 40 weeks. The negative value shows how much time is left until term. At this stage, use the postmenstrual age, which is the axis of the Fenton charts and of NICU targets.
Should I use corrected age for immunization?
No. The immunization schedule follows chronological age, unless your unit has specific indications. The same applies to the introduction of solids.
How long should corrected age be used on growth charts?
Until 3 years. Correcting for a shorter period increases the risk of misclassifying growth failure in former extremely preterm infants.
References
- American Academy of Pediatrics. Newborn and Infant Nutrition Assessment Tools: Term Infant Growth Tools. Available at aap.org.
- Elmrayed S, et al. Preterm growth assessment: the latest findings on age correction. J Perinatol. 2025;45(5):607-615.
- Brazilian Society of Pediatrics (SBP). Follow-up manual for the high-risk newborn. 2nd ed. 2024. Chapters 9 and 15.
- World Health Organization. WHO recommendations for care of the preterm or low-birth-weight infant. Geneva; 2022.
