Make last year same time frame as current date selection an option as a preset calendar.
i.e. - Current month (this year) by just selecting current month (so on jan. 15th would be Jan 1-15). Then make current month last year an option based on only the number of days that have happened so far this month. (so I would want jan 1-15th of last year, not the entire month from last year) to do proper YOY analysis during a given time frame.