Treasurers

Hi there, I'm new to the treasurer role at my church and would like a quick confirmation on ministry shares. In my reading on the CRCNA website and resources passed on to me, I have a fairly comprehensive understanding of how it all works. What I'm curious about is how the exact calculation on membership takes place. For the 2012 year, I know its based on the total membership in the 2012 yearbook, but am I to reduce the calculation by 'inactive members'? On what membership figures is the denomination and classis expecting?