Adding 7/8" to the FINISHED size of the block is the way I was taught.
I draw boxes on the back side of the lighter fabric. If my finished size is going to be 4", then I draw boxes that are 4 7/8". Then I draw a diagonal line through all the boxes and sew a quarter inch on either side of it, then you cut on all the lines. I have pictures at home if anyone wants to see them.