Quoting Tweaky rachie:" my last miscarriage I had a period 28 days after the first day i started to spot, I think everyone is different."
It all depends on how much HCG is in your system, that's why for everyone it's different. You could have a miscarriage at 6 weeks but the baby died at 4 weeks and HCG had already been dropping for two weeks. Or you could have a miscarriage that completes very quickly and it take longer for the HCG to drop completely. HCG is what suppresses the ovaries during pregnancy and your body won't know you're not pregnant anymore until there's no more HCG. I had a late miscarriage more than two weeks ago and I'm still getting positive HPTs. It's going to be awhile before I get another period. This is why doctors say to wait at least one cycle to TTC because conceiving immediately after miscarriage makes dating the pregnancy more difficult.