Both are used to count months, but "달" is often used in spoken.:) \^o^/

They both are counters for months, BUT: 달 is used with native Korean numbers (한, 두, 세, 네, 다섯...) eg. 한 달 개월 is used with Sino/Chinese numbers (일, 이, 삼, 사, 오...) eg. 일 개월

Almost same. 달: Month 개월(個月): Month(s) I think 개월 is unit of counting months. This month = 이번달(o), 이번 개월(x), 금월[今月] (o)

yes ,달= Month , and 개월=months , noon, ex:한 달=1개월, it means a month