Corrected Age Calculator
Work out a premature baby’s corrected (adjusted) age from the birth date and original due date, alongside chronological age.
How it works
corrected age = chronological age − time born before the due date · correction applies only to babies born preterm.
Premature babies are often measured by their “corrected” (adjusted) age — their age counted from the original due date rather than the birth date — because their growth and development track closer to when they were due to be born. It is the same as taking the age since birth and subtracting the number of weeks the baby was early. Clinicians typically use corrected age for growth and developmental milestones until about age 2, after which a healthy child has usually caught up; always follow your pediatrician’s guidance.
Worked example
A baby born March 1 with a May 1 due date arrived about 8 weeks 5 days early (a gestational age near 31 weeks). On September 11, the baby is 6 months, 10 days old chronologically, but the corrected age — counted from the May 1 due date — is 4 months, 10 days.
Frequently asked questions
Until what age should I use corrected age?
Most clinicians use it until about 2 years (24 months), and some stop around 18 months, because by then a healthy child born preterm has usually caught up. Your pediatrician will tell you when to switch to actual age.
Which age do I use for milestones and vaccines?
Developmental milestones — rolling, sitting, talking — are judged by corrected age for preterm babies, while vaccinations are given by chronological age from birth. When in doubt, ask your pediatrician.
My baby was born after the due date — do I correct?
No. Correction is only for babies born early. A baby born on or after the due date is tracked by chronological age from birth.
Related calculators
Estimates based on standard formulas and average cycles — every pregnancy is different. This is not medical advice; your doctor or midwife, with an ultrasound, gives the accurate dates and guidance.