How to tell when ovulating? Any tips?

So I’m trying to tell when I’m ovulating because I really don’t think this app is correct. It’s really the only inaccurate thing on here! But I’m not doing this to become pregnant actually, I’m trying to avoid it because my boyfriend and I don’t always wear a condom and other types of BC gave me terrible mood swings, periods, and worsened basically everything else so we mainly use condoms. But I would also like to know how to tell when the time is decided that we want to start having kids! So do you ladies have any tips or knowledge about how to tell? Thanks in advance!