Am i on my period or implantation bleeding?

Implantation bleed: Implantation bleeding happens 6-7 days after ovulation. Ovulation for mos women happens between days 12-16 from the first day of the period, on average 14 days. Therefore implantation bleeding can occur sometime between day 18 at the earliest and 22 at the latest (days 19-20 for most women). Of course there are exceptions but this applies to most regularly menstruating women.