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 nemesis has returned to haunt meeeee!!!” My husband (Japanese) looked at me with great confusion. Clearly he couldn’t understand the severity of this situation. Of course he couldn’t! He’s long since forgotten the struggles of learning Kanji. Pfft. Privileged Japanese guy. (Fun fact, it took me like 2 minutes to recall the word “privileged”. Guess my English also needs work)…
ANYWAY, when I explained the situation to him he looked very underwhelmed and said very matter of factly, “You use がつ when it comes after a number and げつ otherwise.” …I felt stupid. I sat there thinking for a moment… Was I really so blind!? But then, AHA! I had seen a flaw in his ways. “But what about 何月?? Hmmm??? 何 isn’t a number, yet it’s read as がつ” and he calmly replied, “That’s because it’s taking the place of a number; asking for one. You reply with 一月、二月, etc.”
…Welp. I feel really dumb now but empowered with this new knowledge, I won’t struggle with 月 anymore! …I hope.
And maybe someone else has already realized this in the past 6 years since I last was here but if not then I hope that this might help someone else who struggled as I had.