Displaying the Serial Number Behind the Date

Excel handles dates and times numerically. The numbers for dates range from 1 to 2958465, with 1 indicating January 1, 1900, and 2958465 indicating December 31, 9999.

To see the serial number behind a date:
Press Ctrl+` (the ` key is to the left of the 1 key) to change the display of the cell's contents.

To convert a date to its serial number:
Press Ctrl+Shift+~ to change the cell's contents.

Screenshot // Displaying the Serial Number Behind the Date