Here are all the 12 months in Japanese. The Kanji symbol 月 can be read in 3 ways: TSUKI, GETSU, and GATSU. When saying the name of each month, we use only GATSU.
January, ICHI-GATSU

Correct: Ichi-gatsu
Wrong: Hitotsu-gatsu, Hito-gatsu
February, NI-GATSU

Correct: Ni-gatsu
Wrong: Futatsu-gatsu, Futa-gatsu
March, SAN-GATSU

Correct: San-gatsu
Wrong: Mi-gatsu, Mitsu-gatsu
April, SHI-GATSU

Correct: Shi-gatsu
Wrong: Yo-gatsu, Yon-gatsu

I’ve heard someone say YON-GATSU. Is it wrong?

Not completely wrong and it’s understandable. But Shi-gatsu is a common way of reading.
The pronunciations of Shi-gatsu and Ni-gatsu are similar, so if you can’t catch the word in spoken conversation or on a phone, we sometimes say YON-gatsu to make it clear that it points out April.
May, GO-GATSU

Correct: Go-gatsu
Wrong: Itsu-gatsu
June, ROKU-GATSU

Correct: Roku-gatsu
Wrong: Mu-gatsu, Mutsu-gatsu
July, SHICHI-GATSU

Correct: Shichi-gatsu
Wrong: Nana-gatsu
You may hear someone call July Nana-gatsu. The same as Shi-gatsu (April), we sometimes use Nana-gatsu to specify that it means seven. Also, I think the people from Western Japan tend to call the number 7 NANA. They sometimes call July NANA-gatsu and 7 o’clock NANA-ji. It’s a kind of dialect.
August, HACHI-GATSU

Correct: Hachi-gatsu
Wrong: Ya-gatsu, Yatsu-gatsu
September, KU-GATSU

Correct: Ku-gatsu
Wrong: Kyū-gatsu
October, JŪ-GATSU

Correct: Jū-gatsu
Wrong: Tō-gatsu
Novermber, JŪICHI-GATSU

Correct: Jūichi-gatsu
December, JŪNI-GATSU

Correct: Jūni-gatsu
That’s all for the 12 months name in Japanese! Please comment if you have any questions about this post.
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