Neil
I'm not sure what are trying to do exactly. MTD is independant of YTD, though the concept is the same.
If you have MTD (and know what month it is now), you can sum (Jan + Feb +...Last month + MTD)=YTD, but this seems like a long way around.
Period to dates are very easy in transformer/ PPES, why don't use go that route? Plug in the Impromptu report into transformer & Cognos will take care of all the dates.
Bruce