How to Calculate Exact Age and Date Difference

Choose a calendar age or an elapsed-day count according to the question you need to answer.

Use the Age & Date Difference alongside this illustrative example.

A practical example

Between 1 January 2026 and 1 February 2026 there is one calendar month but 31 elapsed days. Converting the month to 30 days would lose a day. For a birthday, use completed calendar years; for a project log, retain the date pair and elapsed days.

Check the result

Check the day and month before calculating, especially when copying a date written as 03/04. Enter an unambiguous calendar date rather than assuming which country’s order the sender used.

Try a comparison

Move only the end date forward by one day. The total-day figure should increase by one, even if the completed-year figure stays unchanged. This is a useful way to distinguish a birthday boundary from continuous elapsed time.

What this does not establish

Age calculations do not determine legal eligibility. An organisation may apply its own reference date and rules for birthdays on leap day.

Report unclear guidance or a result that needs checking.