Measure for XTD Variance

I am trying to create a measure to compare my actual daily values to my forecasted daily values to a dynamic date range.

For example, I have several sheets in my report that look at different date range views of the graph above. Some are YTD, some are QTD and some are snapshots of individual months. 

The green line are the daily actuals and the black line is the forecast. I need a measure to essential compute the variance up until the latest data point of actuals and ignoring future days in the forecast.