Hi,
I would think that you would count the days with light spotting because it is still menstrual blood--just less of it.
Here is a link you may find helpful in calculating your ovualtion:
http://www.babycenter.com/calculators/ovulation/
You can copy and paste into your address line.
Another way to tell when you are ovulating which I have mentioned in several of my posts is to check your vaginal discharge.
When it becomes clear and sticky (like egg whites), you will ovulate within the next 24 hrs.
Good luck
