If you have a 20-21 day cycle when would you have implantation bleeding?

Question

But if never had it before would it start just like that.

Answer 1

Implantation spotting happens 6-12 days past ovulation. And with a 21 day cycle ovulation should happen on about cycle day 7, so implantation would happen 6-12 days after that or sometime between CD 13-19.
Only about a third of all pregnant women have implantation spotting. It is light, pink or brown, only lasts a couple hours, and doesn't require the use of a tampon or pad. It is usually only seen on the toilet paper after using the restroom.
However, my concern with a 21 day cycle would be a luteal phase defect, have you been tested or charted your BBT to find out?

Answer 2

You would notice implantation bleeding anywhere from CD 20 on. However (not to be debbie downer) I'd be concerned with your 20-21 day cycles. Your luteal phase is normally two weeks and that would mean you'd ovulate on CD 7. When I had the same thing my dr told me that it wasn't enough time for the hormones to produce an adequate follicle for conception. Yes you may be ovulating but the egg quality may be poor. If you don't get pregnant within a couple of months or if you've already been trying for a while I'd get your doctor to check you out. Good luck!