Texas Instruments TI-83 PLUS - Manual (Page 463)

TI-83 Plus Applications 460
Finding Days between Dates/Defining
Payment Method
dbd(
Use the date function dbd( (menu item D ) to calculate the number of days
between two dates using the actual-day-count method. date1 and date2
can be numbers or lists of numbers within the range of the dates on the
standard calendar.
Note: Dates must be between the years 1950 through 2049.
dbd( date1 , date2 )
You can enter date1 and date2 in either of two formats.
•
MM.DDYY (United States)
•
DDMM.YY (Europe)
The decimal placement differentiates the date formats.