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MasterMath

Corrected Age Calculator

The corrected age of a premature baby: the age they would be had they been born on their due date. It is the one used to assess development.

Corrected age

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Corrected age—
Actual age—
Weeks early—
Date they were due—
How long it is corrected for—

How this was worked out

    Indicative result. Corrected age is the usual reference for assessing a premature baby's development, but every case is followed by their paediatrician or neonatologist.

    The formula

    corrected age = actual age − weeks early

    Where it comes from

    A baby born two months early has had two months less development than another of the same age born at term. Comparing them against the chart for their actual age would set off every alarm for no reason, so the weeks early are subtracted.

    How to work it out by hand

    1. Subtract the weeks of gestation at birth from the 40 of a full pregnancy
    2. Convert that difference into days
    3. Subtract it from the baby's days of life
    4. The result is the corrected age

    What is worth knowing

    The correction is applied until the age of two, by which point most premature babies have caught up with their peers in weight, height and motor development. From there the actual age is used. Milestones like sitting, crawling or walking should be judged against the corrected age: a nine-month-old born at 32 weeks is compared with a seven-month-old.

    Frequently asked questions

    What is corrected age?

    The age the baby would be had they been born on their due date. It is the actual age minus the weeks they arrived early.

    How long is corrected age used for?

    Until the age of two, when most premature babies have caught up with those born at term.

    Why does it matter?

    Because judging development against the actual age would make the baby look behind when in fact they are exactly where they should be.