Chronological Age Calculator

Enter a date of birth and the test date to get the exact chronological age in years, months and days, the format used for psychological and educational tests.

How to use the chronological age calculator

Enter the child’s or client’s date of birth and the date of the test or assessment. The test date defaults to today. The result is shown in the Years;Months;Days format that scoring manuals use, along with total months and total days.

How to calculate chronological age by hand

  1. Write the test date as year, month and day, with the date of birth underneath.
  2. Subtract the days. If the birth day is larger, borrow one month from the test month and add the number of days in that month (examiners often use 30).
  3. Subtract the months. If the birth month is larger, borrow one year and add 12 months.
  4. Subtract the years.
YearMonthDay
Test date20261017
Date of birth2017314
Chronological age973

This calculator borrows the actual number of days in the previous month, which is how most online scoring systems work. If your manual tells you to always borrow 30 days, the day count can differ by one or two.

Should days be rounded?

It depends on the test. Some instruments use the age in years and months and drop the days. Others round up to the next month when the days are 15 or more. The calculator shows both versions, so follow the rule in your test manual.

Chronological age vs adjusted age

For babies born before 37 weeks, some developmental tests use an adjusted (corrected) age, which subtracts the weeks born early. That correction is usually applied until about age 2. Use the baby age calculator for weeks and months.

Frequently asked questions

What is chronological age?

It is the exact time that has passed since birth, written in years, months and days. It is different from mental age or developmental age, which come from test scores.

How is chronological age written?

Usually as years;months;days, for example 9;7;3 for 9 years, 7 months and 3 days. Some forms use years-months instead.

Do I round days up for testing?

Only if your test manual says so. A common rule rounds up to the next month at 15 days or more, but many tests use days without rounding.

Why does my hand calculation differ by a day?

Some methods borrow 30 days for every month, while this calculator uses the real length of the month. Use whichever method your scoring manual specifies.

Can I use this for adults?

Yes. It works for any two dates, though adult tests usually only need age in years.

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