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Chronological Age Calculator

Enter the date of birth and the test date to get the exact chronological age in years, months and days, written the way test protocols need it (for example 8;4;12). Built for teachers, school psychologists and speech-language pathologists.

Dates

Follow the rounding rule in your test's examiner manual. Many current tests say not to round.

Chronological age

Enter a date of birth and a test date to see the age.

How to calculate chronological age by hand

  1. Write the test date on the top line and the date of birth underneath, as year, month and day.
  2. Subtract the days. If the test day is smaller, borrow 1 month from the test month and add 30 days.
  3. Subtract the months. If the test month is smaller, borrow 1 year from the test year and add 12 months.
  4. Subtract the years. The result is the age in years;months;days.
Example: born 20 Nov 2017, tested 5 Mar 2026
YearMonthDay
Test date202635
After borrowing20251435
Date of birth20171120
Chronological age8315

The 5th is smaller than the 20th, so 1 month is borrowed (March becomes February) and 30 days are added: 35 − 20 = 15 days. Month 2 is smaller than 11, so 1 year is borrowed and 12 months added: 14 − 11 = 3 months. Then 2025 − 2017 = 8 years. The age is 8;3;15.

All calculations run in your browser. No dates are saved or sent anywhere.

Calendar method vs. test-manual method

The calendar method counts the real number of days in each month (28 to 31), so it gives the exact age. The test-manual method is the paper-and-pencil method above, which always borrows 30 days. The two can differ by 1 or 2 days. If you need the result to match a printed protocol or a scoring program, use the method your test manual describes.

Rounding chronological age

Some older tests round up to the next month when the days are 15 or more (some say 16 or more), so 8;3;15 would become 8;4. Many current tests use the exact age without rounding. The calculator shows both when you pick a rounding rule, but the examiner's manual always decides.

Frequently asked questions

What is chronological age?

Chronological age is the exact time a person has been alive, from their date of birth to a given date, written as years, months and days. Teachers, school psychologists and speech-language pathologists use it on test day to find the right norms for standardized tests.

How do you calculate chronological age by hand?

Write the test date and the birth date as year, month and day, then subtract the birth date from the test date, starting with days. If the days don't subtract, borrow 1 month from the test month and add 30 days. If the months don't subtract, borrow 1 year and add 12 months. For example, test date 2026-03-05 minus birth date 2017-11-20 gives 8 years, 3 months, 15 days.

How is chronological age written, for example 8;4?

Test protocols usually write age as years;months or years;months;days, separated by semicolons. So 8;4 means 8 years and 4 months, and 8;4;12 means 8 years, 4 months and 12 days. It is not a decimal: 8;4 is not 8.4 years.

Should I round chronological age up?

It depends on the test. Some manuals round up to the next month when there are 15 or more days (or 16 or more), while many current tests say not to round at all. Always follow the rule in the examiner's manual for the test you are giving.

Why does my hand calculation differ by a day or two?

The hand method borrows a flat 30 days, while the calendar method uses the real length of the month (28 to 31 days). The two can differ by 1 or 2 days. Choose Test manual (borrow 30 days) in the calculator to match a paper protocol.

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