Online Chronological Age Calculator
School psychologists, speech-language pathologists and teachers need an exact chronological age for scoring standardized tests. Enter the date of birth and the date of testing to get the age in Y;M;D format, the rounded age and total months.
- Chronological age (Y;M;D)
- 9;6;26
- In words
- 9 years, 6 months, 26 days
- Rounded to nearest month (≥ 16 days rounds up)
- 9;7
- Total months
- 114.85
Steps
- Test date: 2026-10-17
- Birth date: 2017-03-21
- Subtract days, then months, then years — borrowing a month's actual length when needed → 9 y 6 m 26 d
Worked example
Example: born March 21, 2017, tested October 17, 2026
- Days: 17 < 21, so borrow a month (September has 30 days): 17 + 30 − 21 = 26 days
- Months: (10 − 1) − 3 = 6 months
- Years: 2026 − 2017 = 9 years
Chronological age = 9;6;26 (rounds to 9;7).
Formula
CA = Test date − Birth date (years; months; days)
Some test manuals say to borrow 30 days for every month; others use the actual month length. This calculator uses actual calendar months — check your manual's rounding rule, since some never round up.
Frequently asked questions
What is chronological age?
The exact time a person has been alive, measured from birth to a given date — as opposed to developmental, mental or adjusted age.
How do I round chronological age?
Many tests round up a month when the days are 16 or more. Others truncate. Always follow the specific test manual.
Should I use adjusted age for premature children?
For children born before 37 weeks, many screeners (like the ASQ) use adjusted age until 24 months. See the adjusted age calculator.
Last reviewed October 17, 2026 · Calculations run in your browser; nothing you enter is sent to a server.