I've read that 20-30% of women experience implantation bleeding and that it is difficult to tell the difference between IB and your period... so how are you to know? Are there ANY defining characteristics? I am WAY off counting and think I missed O all together but today I got three bright red spots. I feel like I read somewhere that bright red blood was not implantation bleeding, but dark brown is more characteristic, but now I can't find any evidence online of that being true. If it is AF, then that means I o'd on day 8, giving me a 23 day cycle.