Last, this, next month
The sen-, kon- and rai- of the week words applied to months, with no exceptions.
sengetsu
last month
先月 せんげつ
Last month, for recaps. It uses the same sen- as senshuu, so it pairs with past tense.
casual
sengetsu hikkoshita n da.
I moved last month.
先月引っ越したんだ。
polite
sengetsu hikkoshita n desu.
I moved last month.
先月引っ越したんです。
kongetsu
this month
今月 こんげつ
This month, for budgets, schedules and deadlines. It uses the same kon- as konshuu.
casual
kongetsu hikkosu n da.
I'm moving this month.
今月引っ越すんだ。
polite
kongetsu hikkosu n desu.
I'm moving this month.
今月引っ越すんです。
raigetsu
next month
来月 らいげつ
Next month, for plans and deadlines. It uses the same rai- as raishuu.
casual
raigetsu hikkosu n da.
I'm moving next month.
来月引っ越すんだ。
polite
raigetsu hikkosu n desu.
I'm moving next month.
来月引っ越すんです。