[Question] How to figure out BPM

This is probably a really stupid question to ask, but I’d rather embarrassed myself than learn the wrong stuff. I tend to play too fast without a metronome, so I’m practicing to go according to the beat. I know the key is to start slow and increase the speed gradually, but I have trouble manually figuring out when I should stop increasing to match the original tempo of the song. How do I figure out what any song’s BPM is with a metronome?

ETA: Potential dyscalculic here. I tend to mess up counting, and I have no time awareness. I understand I’ll have to suck up and do the counting, but the poor time awareness might also hinder me. I’m not sure if that’s why I haven’t been able to do it, or whether I’m just doing it all wrong.