Chronological age calculator
Date of birth and test date in, exact age out — years, months and days, the years;months notation record forms use, and age in months for norm tables. Add gestation at birth for a corrected age.
- Rounding
- Days never round up
- Prematurity
- Corrected to 40 weeks
- Runs
- In your browser only
Use the tool
Dates are calculated in your browser and never sent anywhere.
Enter a date of birth to see the age.
How the age is worked out
The difference is taken in whole years, months and days. When the day of the test is earlier in the month than the day of birth, a month is borrowed and the days are counted from the length of the month before the test date — the same hand method most test manuals describe, so the result matches what you would get on paper.
Days are never rounded up into a month. If your manual asks you to round, do it from the figure shown; the tool deliberately does not guess which convention a given test uses.
Corrected age for prematurity
Enter the gestation at birth in weeks. For a child born before 37 weeks, the tool subtracts the weeks short of 40 from the chronological age and shows both figures side by side. Correction is conventionally applied until 24 months of chronological age; the tool flags when the child is past that, and your test manual decides whether the corrected or chronological figure is the one to use.
Copy it into the record form
The copy button gives you one line with the test date, the age in words, the years;months notation and the age in months, ready to paste into a test record form or a note.
Questions, answered
Which date convention does it use?
Dates are read as calendar dates (year, month, day) with no timezone arithmetic, so a date of birth entered as 12 April is 12 April wherever you are. The date pickers show your device's own format.
Does it store the date of birth?
No. Nothing on this page is saved or sent. Refreshing the page clears it. The test date simply defaults to today.
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