Preterm Baby Corrected Age Calculator
Calculate the corrected (adjusted) age of a premature baby by accounting for weeks born early. Use this when tracking developmental milestones, growth charts, or cognitive benchmarks for preterm infants.
Last updated: September 2026
Formula below · 3 sources (aap.org, healthychildren.org, Wikipedia) · Updated Sep 2026
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About this calculator
Premature babies are born before 37 weeks of gestation, so their developmental clock starts earlier than full-term peers'. Corrected (adjusted) age removes the head start: corrected age = chronological age (months) − weeks born early ÷ 4.345, where weeks born early = 40 − gestational age at birth and 4.345 is the average number of weeks in a month. The same corrected age is used for developmental milestones, growth charts and feeding expectations; the AAP does not apply different multipliers for different assessments or for birth weight. Babies born at 37 weeks or later are term, so the calculator returns their chronological age unchanged. A negative result means the baby has not yet reached their original due date (for example −1.5 months = about 6.5 weeks before term). Correction is normally used until about 24 months corrected age, longer for babies born very early.
How to use
Example: A baby born at 32 weeks gestation now has a chronological age of 6 months. Step 1 — weeks premature: 40 − 32 = 8 weeks. Step 2 — convert to months: 8 ÷ 4.345 ≈ 1.84 months. Step 3 — subtract: 6 − 1.84 ≈ 4.16 months corrected age. This means the baby's milestones and growth should be compared to a typical 4-month-old, not a 6-month-old.
Frequently asked questions
What is corrected age for a premature baby and why does it matter?
Corrected age (also called adjusted age) is the age a preterm baby would be if they had been born at 40 weeks gestation. It matters because premature babies spend time outside the womb that was meant to be spent developing in utero. Comparing a preterm infant's milestones to same-chronological-age peers without correction can falsely suggest developmental delays. Most pediatricians use corrected age for assessments until the child is 2–3 years old.
How long should I use corrected age when tracking my preterm baby's development?
Pediatric guidelines generally recommend using corrected age for developmental and growth assessments until at least 24 months corrected age, and sometimes up to 36 months for babies born very early (before 28 weeks). After that point, most children have caught up sufficiently that the distinction becomes clinically less significant. Very low birth weight infants (under 1,500 g) may benefit from correction for slightly longer. Always follow your pediatrician's guidance for your specific child.
Should I use a different corrected age for growth than for development?
No. The AAP and growth-chart guidance use the same corrected age — chronological age minus the weeks born early — for growth (length, weight, head circumference), feeding and developmental milestones. Extra multipliers for growth, feeding or very low birth weight that some tools apply have no basis in the guidelines. What does differ is how long correction is continued: usually to 24 months, and sometimes to 36 months for babies born before about 28 weeks.