Page 198 - Easy Japanese - Learn to Speak Japanese Quickly! (TUTTLE)

The classifier for counting weeks is -shūkan. It is combined with the Chinese
numbers. There is no naming classifier for weeks. Note the sound change (s →
ss) with one, eight and ten and the choice of alternatives for four, seven, and
nine.
1 is-shūkan 4 yon-shūkan

7 nana-shūkan 8 has-chūkan
9 kyū-shūkan 10 jus-shūkan

The naming classifier for months is -gatsu, and when naming dates, the month
precedes the day. The counting classifier is -kagetsu. Both are combined with
the Chinese numbers. Note the sound change /ka/ → /kka/ with one, six, eight,
and ten.

Naming Months
Ichi-gatsu 一月 January

Ni-gatsu 二月 February
San-gatsu 三月 March

Shi-gatsu 四月 April
Go-gatsu 五月 May

Roku-gatsu 六月 June
Shichi-gatsu 七月 July

Hachi-gatsu 八月 August
Ku-gatsu 九月 September

Jū-gatsu 十月 October
Jūichi-gatsu 十一月 November

Jūni-gatsu 十二月 December
nan-gatsu 何月 what month

Counting Months
ik-kagetsu 一ヶ月 one month

ni-kagetsu 二ヶ月 two months
san-kagetsu 三ヶ月 three months

yon-kagetsu 四ヶ月 four months
go-kagetsu 五ヶ月 five months