I have an excel spreadsheet that I download from a vendor that has the dates
listed as MAY/17/2010 - JUL/31/2011 and I am not able to use my existing
formula to figure out the number of months between two dates.

I was using =(YEAR(cell for end date)-YEAR(cell for start
date))*12+MONTH(cell for end date)-MONTH(cell for start date) which was
working great but now since the vendor changed their date format it won't
work. I have even tried to format those cells to yyyy-mm-dd but they stay as
they are above.

Any help would be greatly appreciated because I don't want to have to retype
all the dates each time to get the month formula to work.

Thank you in advance.

Kim