Have got a real memory block on this one and it seems to be such a basic question nobody else seems to be asking it
CD1 is the first day of my period, yes?
So this would be Dec 8th
CD26 is the first day of the next period
this was 2nd Jan
Is this a 26 day cycle and CD26 is also CD1 and I count the day twice or a 25 day cycle and each day is only counted once?