Health Pregnancy

Baby age calculator

Last reviewed 23 Aug 2026 ·Method: chronological age from date of birth; corrected age subtracts weeks born before term.

Date of birth

On this date

Weeks born early

For corrected age

Age —

From , less 0 weeks early

Days old —

Weeks old —

Months old —

Corrected age —

First birthday —

Corrected age for preterm · chronological for vaccines

Corrected age is the standard way to assess development in babies born preterm, and is normally used until about two years.

Baby age is usually given in weeks for the first few months and months thereafter. For a baby born preterm, corrected age subtracts the weeks born early — a six-week-early baby who is 8 weeks old has a corrected age of 2 weeks.

How to work out baby age

1 Enter the date of birth.

2 The second date defaults to today; change it to check any date.

3 Add the weeks born early if the birth was preterm.

4 Use corrected age when comparing against developmental milestones.

Corrected age exists because development runs from conception rather than from birth. A baby born ten weeks early has had ten fewer weeks to grow, and expecting them to sit, smile or crawl on the chronological schedule sets an unfair and misleading benchmark. Clinicians use corrected age for milestones until around two years, by which point the gap has largely closed. Chronological age remains the right figure for vaccination schedules, which follow time since birth rather than developmental stage.

Questions

What is corrected age? −

Chronological age minus the number of weeks born before 40 weeks. It is used to assess development in preterm babies.

Until when should I use corrected age? +

Do vaccinations follow corrected age? +

How many weeks in a month? +

Why is age given in weeks at first? +

Sources

CDC — developmental milestones

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