True When we finally started trying to have kids we found this out too. Knowing the cycle well should be enough
Apparently there are some pretty advanced ways that aren’t invasive to discern the fertile portion of the cycle too. Really interesting. Personal responsibility, discipline and awareness for the win (yet again)
I have a cycle calendar app that tells me, and I've begun to notice different things regularly line up at certain parts of my cycle, so I will eventually just know where I'm at without the app.