How long should I wait?.

Dee
I took my last BC pill last week, I'm on my period now. I do not plan on going back on BC, I'm going to do the FAM from now on. How long should I wait before I trust what the app says my safe/unsafe days are?. I'm avoiding pregnacy for now. I've never had to keep track of this and I was always bad at taking my pill. Pls help