Help with a measure.

Hi

I have a measure for Occupancy per course as follows

Occupancy Forecast (%) =
DIVIDE(
SUMX('CTS Forecast Course Volume', [Forecast Total Attendees]),
SUMX('CTS Forecast Course Volume', [Capacity per Course] * [Trainer Ratio] * [Volume])
)

This gives me an Occupancy percentage per course (because of the SUMX) and I can summarize by month as each course is linked to a date table

I want to create a ytd measure of the same

I am using a custom ytd measure as our year ends 31/03 so for example 

YTD Forecast Total Attendeed = CALCULATE([Total Forecast Attendees],DATESYTD('DateMASTER'[Date],"31/03"))

where Total Forecast Attendees = sum(Forecast Attendees)

Any ideas on the YTD calculation needed for the Occupancy Forecast % YTD?