CD21 tests?

Ge

Just got back from the docs and hubby is going to have semen analysis and I've been referred for day 2 and 'day 21 bloods'...

I heard day 21 is if you have a regular 28 day cycle as it relates to after ovulation, how will I know when to have it.. I'm regular(ish) to within a few days normally, but 32 ish day cycle. Dont wana mess the test up by having it on the wrong day...

Any help appreciated ladies! 😊