In Excel dates are really just numbers formatted to look like dates. These numbers are commonly referred to as the date serial number. The date serial number is the count of days starting from a base date. In Windows Excel the default base date is January 1, 1900. So, January 1, 1900 is date serial number 1.

Jan 1 1900 = date serial number 1
Jan 2 1900 = date serial number 2
Jan 3 1900 = date serial number 3
Jan 4 1900 = date serial number 4
Jan 5 1900 = date serial number 5
etc
etc
Jan 1 1975 = date serial number 27395
Jan 1 2000 = date serial number 36526
Jan 1 2014 = date serial number 41640

You can see the date serial number by entering some date in a cell and then changing that cells format to General or Number.

This makes it possible to do math operations on dates such as =A2+7.

Thanks for the feedback!