To calculate the month to date value of the prior year, you need to filter the order date to be between the first day of the same month of the previous year and the same day of the previous year. You can use the calculated fields [Calc1] and [Calc2] to get these dates. [Calc1] returns the date that is one year before today, and [Calc2] returns the date that is the first day of the month of [Calc1]. By using these fields in the filter condition, you can get the desired result.