@Hanbanxx - My cycle is only looking a little bit longer, with both of my MCs it was 5 weeks rather than my usual 29 days, but I think to be expected. MY HCG levels were at 300 about 2 days before I started to miscarry this time around.
But yes, CD1 is day 1 of your MC. I think I ovulated on CD19/20 this cycle.
The only bit of advice I would give you, is that after my 1st MC, with the exception of the first cycle, they were a bit longer. I was using the clear blue advanced but on our 2nd cycle despite my "peak fertility" appearing a few days later than normal, I was still a week late for AF (BFN on PT too).
On my third cycle, I was so late ovulating I gave up on my Clearblue Advanced as there were so many days of "high fertility" but no "peak".
On my 4th cycle after my MC (which we got pregnant on) I started using the cheapies alongside my Clearblue. The ability to carry on testing for LH after my "peak" meant that I was able to realise that I was attempting to ovulate, failing to do so and then successfully managing it on attempt #2 a few days later - but the Clearblue wasn't able to pick up on this.
So I would be patient with your cycles after your MC, they can be a bit off but you will ovulate. It meant that out of our 4 cycles after miscarriage, we were only DTD at the right time twice.
I hope that helps! X