Formula
The count walks from the earlier birthday to the later one:
Age difference = calendar years, months, and days
The age page measures one person up to a chosen date. Chronological age is a decimal year count.
Assumptions
- The later birthday is on or after the earlier one.
- Time of day is ignored.
Worked example
Birthdays on March 15, 1994 and June 1, 2000 are 6 years, 2 months, 17 days apart.
Input definitions
- Earlier birthday
- The first of the two dates.
- Later birthday
- The second date.
Limitations
This is a planning estimate for school or a calendar. It is not an official transcript, an attendance record, or a payroll ruling.
Questions
Is this the number of days?
No. It keeps years and months. The date difference page counts days.
What if I swap the dates?
Put the earlier birthday first. The form rejects a reversed pair.