Hi Nitika ,
I used a start date of 15-Nov-2010 , and checked the DATEDIF function result for all dates thereafter , starting with 16-Nov-2010 ; it starts with 1 , goes up to 29 , and then resets to 0 , goes up to 30 and repeats this behaviour. When the dates are between 1-Jan-2012 and 14-Jan-2012 , the return values are from 130 to 143.
Again , 15-Jan-2012 and after , the behaviour is consistent , varying between 0 and a maximum of 30 each month ( some months the maximum value is 27 , others 28 , 29 and 30 ). But the inconsistent behaviour repeats from 1-Jan-2016 and 14-Jan-2016 , when the return values are again between 130 and 143.
Every leap year results in this inconsistent behaviour.
Of course , other combinations of start and end dates give other results !
Since this is an undocumented and unsupported function , I think you have to live with this inconsistent behaviour.
Narayan