There is difference between Zoho Sheet and Microsoft Product in results of YEARFRAC formula.  You can download a test file from this  site( http://plugtest.opendocsociety.org/doku.php?id=scenarios:20100415:yearfrac ) and 

result is this( http://www.slideshare.net/slideshow/embed_code/16726545?startSlide=30 ).

I do not know which one is right but there is difference.