I'm trying to put together an MDX Calculation that figures out the MTD of last years month.  So right now it woudl figure out MTD up to Sept 9th, 2013.  

I've tried the following but it doesn't work (I'm feeding it the date through a tool so it won't be hard coded).

Sum(PeriodsToDate([OrderDate].[OrderDate].[Month],ParallelPeriod([YEAR], 1, [OrderDate].[OrderDate].CurrentMember)),[Measures].[BookedAmt])


I figure i'm way off, any help would be greatly appreciated.

Thanks,