Pivot table - formula/format to filter by month and year

I have data set that contains several rows of variables, including the start date (mm/dd/yyyy) of that entry. It does not contain separate fields for month and year. I want to be able to filter my pivot table by month and year - so I can view all the data in, for example, October 2013, or just 2014.

My solution was to create 2 extra columns. In the first column, I had the formula where it was = to the start date cell, but then custom formatted to just "mmm" to display, and in the next column the same except formatted to display "yyyy." But Excel recognized the entire date, not just the month and year (which was displayed), so when I went to filter, it pulled up as many 2014's as were entered in the data with distinct dates.

Any other solutions?

Ok - just found my answer... for those interested:

I could use the "Group" function, but I don't have the dates actually in my pivot table... I would have to add the date field and that really seemed to mess things up. I was on track with my thinking to add columns to the source data, just didn't know the formula... I've learned I can use DATE() and YEAR() functions, which will allow me to add my filters to my pivot table.

BTW, I also don't have slicer, FYI - which looks like it would've been another option...