Chronological Age Calculator
Find exact age in years, months and days on a test date, as used in speech, psychology and school assessments.
About the Chronological Age Calculator
Standardised tests look up scores by chronological age, so it must be calculated the way the manual specifies. The usual method subtracts the birth date from the test date, borrowing 30 days for a month and 12 months for a year when needed. Some manuals round 15 or more days up to the next month; check yours.
The formula
Age = test date − birth date, borrowing 30 days or 12 months
Worked example
Example: Chronological age = 0 years 2 months 14 days
- Inputs: Date of birth: 1 January 2026; Test date: 15 March 2026; Round days: No.
- Formula: Age = test date − birth date, borrowing 30 days or 12 months
- Subtract day, month and year 2026-3-15 − 2026-1-1
- Borrow 30 days or 12 months when needed 0 y 2 m 14 d
- Result: Chronological age = 0 years 2 months 14 days
Questions people ask
Why 30 days, not the real month length?
It's the convention most test publishers use, so results match their norms tables.
Is this different from the age calculator?
It follows the testing convention; the age calculator uses true calendar months.