Try this…Type a date into a cell using one of the formats the Excel recognises (such as 25-Dec-2013, 25/12/13 or 12/25/13). Now change the format of the cell to General and you should see the number 41633 in the cell.
So what’s going on? What is the connection between 25th December 2013 and 41633?
The number in the cell represents the number of days since 1st January 1900. This is Excel’s “base date” – Excel doesn’t recognise dates before this date. Note: Excel for Mac used to use 1st January 1904 as the base date but this changed with Excel 2011 which now aligns itself with the Windows configuration (i.e. 1st January 1900).
A similar thing happens with times..type 18:00 (i.e. 6:00PM) into a cell, change the format to General and you should see the value 0.75 in the cell. The number represents the proportion of a day (i.e. 24 hour period) expressed as a percentage. In other words, 6:00PM is 75% through the day (24 hour period).
Excel converts dates and times to numbers for several reasons, the main one being to be able to do calculations. Another reason is to count the number of times a specific date occurs in a range of cells, when the range has been formatted as date/time (for example, dd/mm/yyyy hh:mm). I’ve written another tutorial on this subject