I'm on the Pill and I still only have a rough idea. Obviously I know it'll start sometime in my week off, but I really haven't noticed a pattern. I used to take Logynon, and that really was regular to the hour, but with Cilest? Nope. And I rarely take my Pills properly, so on a month-to-month basis, I'm not very regular either. I'm all ways taking a few/a week/an extra month's worth of pills to avoid having an inconvenient period.