When to use げつ vs がつ

[Arzar33]

My nemesis, 月, and how to overcome his evil ways

So if anyone was around many years ago, they may (although probably not) remember that my wall of shame was ALWAYS plastered with some vocabulary word containing the 月 kanji. The reason for this was that I would always get mixed up between the readings がつ and げつ. Some lovely friends always made fun of me for it and yet no one at the time could give me any hints about how to recall which reading to use when. :') WELL, when I was reintroduced to this vocabulary I shouted in agony. “Noooo! My nem…