It’s sometimes called the rhythm method, natural family planning, or fertility awareness. It relies on having sex at certain times around your egg being released to make sure you either don’t get pregnant or you do get pregnant. You need to have regular periods in order to use it and you need to be hyperorganized in order to make sure it works.
Pros: It’s just you keeping track of your body (and now with more and more apps, it’s even easier).
Cons: If your primary goal is to NOT get pregnant, there are WAY more effective ways of preventing that from happening.