Talking About the Scheduled Time

がつ [gatsu] and つき [tsuki] both mean 'month', but they're different words:

• つき [tsuki] is what we say when we talk about a month as a concept.
• がつ [gatsu] is what we use to identify a specific month.

Months in Japanese: number word + がつ [gatsu]

• いちがつ [ichi gatsu] January
• にがつ [ni gatsu] February
• さんがつ [san gatsu] March
• しがつ [shi gatsu] April
• ごがつ [go gatsu] May
• ろくがつ [roku gatsu] June
• しちがつ [shichi gatsu] July
• はちがつ [hachi gatsu] August
• くがつ [ku gatsu] September
• じゅうがつ [jū gatsu] October
• じゅういちがつ [jū ichi gatsu] November
• じゅうにがつ [jū ni gatsu] December

The two counter words for 'day' are か [ka] and にち [nichi]

Days 2 through 10 use native Japanese numbers + か [ka]

• ふつか [futsu ka] Day 2
• みっか [mit ka] Day 3
• よっか [yot ka] Day 4
• いつか [itsuka] Day 5
• むいか [mui ka] Day 6
• なのか [na no ka] Day 7
• ようか [yō ka] Day 8
• ここのか [koko no ka] Day 9
• とおか [tō ka] Day 10

4 Exceptions for Days:

• ついたち [tsuitachi] Day 1
• はつか [hatsuka] Day 20
• じゅうよっか [jū yokka] Day 14
• にじゅうよっか [nijū yokka] Day 24

誕生日はいつですか [tanjōbi wa itsu desu ka]
When is your birthday?

• 誕生日 [tanjōbi] means "birthday"
• いつ [itsu] means "when"
• Literally means "Birthday, when is it?"

１月１７日 [ichi gatsu jū shichi nichi]
January 17th

• １月 [ichi gatsu] means "January"
• １７日 [jū shichi nichi] means "17th"

２月２４日です [ni gatsu nijū yokka desu]
It's February 24th.

• ２月 [ni gatsu] means "February"
• ２４日 [nijū yokka] means "24th"

• A: 誕生日はいつですか
  When is your birthday?
• B: 3月30日です [san gatsu san jū nichi desu]
  It's March 30th.
• B: じゃあ、誕生日は明日ですか
  So, is your birthday tomorrow?
• A: はい [hai]
  Yes
• B: 誕生日おめでとうございます
  Happy birthday!