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Calculate corrected (adjusted) age for preterm infants: chronological age minus weeks born before the due date. Use for gestational dating context, milestone expectations, and early growth charts—immunizations still follow actual birth date.
Last updated: June 4, 2026
Corrected age
2 months, 3 weeks
11 total weeks
Chronological age
4 months, 1 week
Moderately preterm (4–7 weeks early). Use corrected age for milestone and growth expectations until your clinician transitions to chronological age. Typically adjust until 12–18 months corrected.
Educational tool only. Immunizations follow chronological age. Confirm growth chart plotting and milestone expectations with your pediatrician or NICU follow-up team.
Demo (~6 weeks early, ~4 mo chronological)
2 months, 3 weeks
Corrected vs 4 months, 1 week chronological
3 weeks early (late preterm)
2 months, 3 weeks
3 weeks prematurity
8 weeks early (~32 weeks GA)
2 months, 3 weeks
GA at birth ~32 weeks
| Prematurity | Typical adjustment period | Teaching note |
|---|---|---|
| < 4 weeks early (late preterm) | ~12 months corrected age | Often discontinue adjustment around first birthday |
| 4–7 weeks early | ~12–18 months corrected age | Many clinics use corrected age through 15–18 months |
| ≥ 8 weeks early (< 32 weeks gestation) | ~18–24 months corrected age | NICU graduates may need longer adjustment on growth charts |
| Born at or after due date | Not indicated | Use chronological age for development and growth |
| Domain | Use | Example |
|---|---|---|
| Developmental milestones | Corrected age | Rolling, sitting, walking expectations |
| WHO/Fenton preterm growth charts (early infancy) | Corrected age | Plot weight/length/head circumference vs corrected weeks |
| Immunizations | Chronological age | CDC schedule from actual birth date |
| Early intervention eligibility (U.S.) | Often chronological with prematurity exception | State Part C rules vary — ask your coordinator |
| Introducing solid foods | Usually corrected ~6 months | Readiness signs follow neurologic maturity |
| Sleep training discussions | Clinician preference | Some use corrected 4–6 months for preemies |
| Milestone | Typical window |
|---|---|
| Social smile | 6–10 weeks corrected |
| Head control / tummy time | 2–4 months corrected |
| Rolling | 4–6 months corrected |
| Sitting without support | 6–8 months corrected |
| Crawling | 7–10 months corrected |
| Walking independently | 11–15 months corrected |
Weeks prematurity = (Due date − Birth date) in whole weeks
Corrected age = Chronological age − Weeks prematurity
If birth is on or after due date, prematurity = 0 (term infant)
Chronological age: 120 days (4 months, 1 week since birth)
Weeks born before due date: 6 weeks (42 days)
Corrected age: 120 − 42 = 78 days → 2 months, 3 weeks
Estimated gestational age at birth: ~34 weeks (40 − 6)
Tell daycare and therapists: corrected age is 2 months, 3 weeks, not 4 months, 1 week alone.
Prematurity: 8 weeks → estimated 32 weeks gestation at birth.
Corrected age: 2 months, 3 weeks vs chronological 4 months, 3 weeks.
Very preterm pattern (≥8 weeks early). Use corrected age when comparing to ASQ/developmental screening windows your pediatrician provides. Many teams extend corrected age to 18–24 months for development and growth.
Education only. Not for diagnosing developmental delay or failure to thrive. Use your pediatrician’s growth chart choice, NICU discharge plan, and early intervention team for decisions.
For NICU parents, pediatric trainees, and lactation teams