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Corrected Age for Preemies

Adjust a preemie's age for how early they were born.

How it is calculated

Corrected age removes the weeks a baby was born early from their age counted from the birth date. weeks premature = 40 − gestation at birth and corrected age = chronological age − weeks premature. Both inputs are in weeks: the age since birth (so 4 months is about 17 or 18 weeks) and the weeks of pregnancy completed at birth. Forty weeks is used as full term. The age since birth cannot be negative, and the gestation must be at least 20 and below 40; a baby born at 40 weeks or later is not premature, so those inputs show no result. Results are shown in whole weeks, so enter whole weeks. The tool does not hold the corrected age at zero: for a baby younger than the weeks premature the figure becomes negative, meaning the due date has not been reached yet.

Worked example

A baby was born at 32 weeks of pregnancy and is now 20 weeks old by the calendar. Weeks premature: 40 − 32 = 8. Corrected age: 20 − 8 = 12, shown as 12 weeks with 8 weeks premature below it. So the baby's development is best compared with that of a 12-week-old born at term, roughly 3 months, even though the calendar says almost 5 months.

Try this example →

Common mistakes

  • Entering the age in months. The field is in weeks, so 4 months is about 17 weeks, not 4.
  • Entering the due date week or the number of weeks until term instead of the gestation at birth. Enter how many weeks pregnant the mother was when the baby was born, such as 32.
  • Entering 40 or more for a baby who was born close to term. The tool only handles premature births, so a gestation of 40 shows no result, and 39 gives just 1 week of correction.
  • Entering the current age in weeks since conception. Use the age counted from the birth date only.
  • Applying corrected age indefinitely. The result is for comparing early milestones, and the tool does not say when to stop correcting; ask the child's doctor.

Sources

About this calculator

Corrected age (also called adjusted age) accounts for how early a baby was born by subtracting the number of weeks of prematurity from their chronological age: corrected age = chronological age − (40 weeks − gestational age at birth). A baby born at 32 weeks who is 4 months old chronologically, for instance, has a corrected age closer to 2 months, since they missed 8 weeks of in-utero development.

Pediatricians use corrected age rather than chronological age when tracking a premature baby's growth, motor skills and developmental milestones on standard growth charts for roughly the first 2 years of life, because comparing a preemie's raw birth-date age against full-term norms would make normal development look delayed. Parents of preemies use it for the same reason — to set realistic expectations for milestones like rolling over, sitting up or first words.

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