I'm gonna get hammered here because this is Lemmy and anything even loosely associated with Natural Family Planning is going to get down voted.
There are very specific and narrow methods that work well (not perfectly, obviously). I won't quote and statistics here.
To start up top, if you want to use any method of birth control, do it. It's up to you entirely, I don't judge anyone at all.
Also, anything related to the calendar method, day counting, or any such nonsense fuckin sucks. Some like to rope that into natural family planning because they are super simple... But super simple doesn't work.
If anyone is interested in learning about one that actually has scientific backing, it would be the Billings Ovulation Method. But it's not day tracking or anything... You need to do some work. You need to learn about it, learn your own body, and be diligent. And most importantly, use alternative methods when you aren't sure.
Again, I'm willing to bring on the downvotes, but I hope people research before assuming it's all bullshit.
And just to be clear: If you want something easy, use birth control.
As an edit: I want to fully acknowledge the gap between typical use and perfect use. My wife and I are certainly in the perfect use category... Her dad is a doctor and we are well aware of all the science behind it. If you aren't going to put in the work, the method is NOT for you. At all.