Monthly Totals

I can't figure out how to report by month, on a saved report. Right now it's a year to date report, by expense category. I need to go back and see the monthly totals of these exact items in the saved report, but by a prior year, totaled by month. The saved report, but saved to a new report subtotaled by month of a certain whole year. I can put in custom dates of 1/1-12/31 of the year, but can't get by month?