Guides

Calculating age by hand

Write the later date above the earlier one. Subtract days, then months, then years. If days go negative, borrow the length of the previous month. If months go negative, borrow 12 months from the years.

Chronological vs biological age

Chronological age is time since birth. Biological age describes how the body is functioning and can differ. Test norms and forms almost always ask for chronological age.

Recording age on assessment forms

Use the exact test date, not the date you score the test. Write the age in the format the manual asks for, and keep the birth date and test date on the record so anyone can re-check the result.

Common date mistakes

Typical errors are counting 30 days for every month, forgetting leap years, swapping day and month, and rounding months up. A calculator removes most of them.

Counting days to a birthday

Find the next occurrence of the month and day, then subtract today. If the date has already passed this year, use next year. A 29 February birthday falls on 1 March in non-leap years here.