Hello Natnicha

The way I've attempted this in the attached workbook is to create separate rank calculations for each month then subtract November's rank from December's.

I hope this helps.

Steve

just read your original post again, I fixed this to November and december but to get present month - previous month you'd need this for current month:

and this for previous:

NOTE they won't work with superstore data as that only goes to December 2014 and the TODAY() function will be the current date.