Why would you need to calculate dates from 1904 instead of 1900?

Hi Elizabeth, Welcome to the forum, Thank you for your question, in answer; When Excel on the PC, perceives a date entry, it will transform that entry to a value which is a count of the number of days from 1/1/1900. However in relation to your question; I have never heard of PC versions calculating dates from 1904, however the Mac version does use the 1904 date as a start, As the Mac version preceeded the PC version perhaps it is the original method, but when the PC version was created 1900 was chosen as it was not a leap year, however in the early versions of Excel it was perceived as a Leap Year (a major bug) this was corrected in later versions. So my answer would be if you are working with colleagues who have the Mac version of Excel the sheets will have a date incompatibility if transfered between PC and Mac. If this has not answered your question you could come back with more information on this. However if it has, please click the Resolved link, best regards Pete.