Months in Japanese are mostly just number + 月 (with two exceptions, 四月 and 九月), but calendar days from the 1st–10th (plus the 14th, 20th, and 24th) use their own irregular words you simply have to memorize.
This guide is for N5–N4 learners who want to say dates out loud without guessing. After reading, you will know which day-words to memorize as whole units, and which ones you can build yourself.
Quick summary: Months follow number + 月 with two exceptions, but calendar days 1st–10th, 14th, 20th, and 24th are irregular words you must memorize separately.
| Number | Day of the Month (〜日) | Month (〜月) |
|---|---|---|
| 1 | ついたち (tsuitachi) | 一月 いちがつ (ichigatsu) |
| 2 | ふつか (futsuka) | 二月 にがつ (nigatsu) |
| 3 | みっか (mikka) | 三月 さんがつ (sangatsu) |
| 4 | よっか (yokka) | 四月 しがつ (shigatsu) — not よんがつ |
| 5 | いつか (itsuka) | 五月 ごがつ (gogatsu) |
| 6 | むいか (muika) | 六月 ろくがつ (rokugatsu) |
| 7 | なのか (nanoka) | 七月 しちがつ (shichigatsu) |
| 8 | ようか (youka) | 八月 はちがつ (hachigatsu) |
| 9 | ここのか (kokonoka) | 九月 くがつ (kugatsu) — not きゅうがつ |
| 10 | とおか (tooka) | 十月 じゅうがつ (juugatsu) |
| 14 | じゅうよっか (juuyokka) | — |
| 20 | はつか (hatsuka) | — |
| 24 | にじゅうよっか (nijuuyokka) | — |
- Why English ‘the 4th’ Doesn’t Prepare You for 四日 and 四月
- The One-Question Test: Is This One of the Special Days?
- Building Months: 一月 to 十二月 and the Two Exceptions
- Building Calendar Days: ついたち, はつか, and the Irregular Set
- 何曜日 vs 何日: Two Questions English Squeezes Into ‘What Day’
- FAQ: Dates, Days, and Months in Japanese
- Quiz: Test Your Dates, Days, and Months
- Summary
Why English ‘the 4th’ Doesn’t Prepare You for 四日 and 四月
A pattern that looks regular until it suddenly isn’t
English ordinal numbers are mostly predictable. You add “-th” to a number, with only three small exceptions at the start.
Because of this, English speakers expect Japanese dates to settle into a pattern quickly too. But calendar days from the 1st to the 10th use a separate set of words.
These words come from native Japanese number roots, not the counting numbers you would expect before 日. Months look more regular, but two of them quietly break the pattern as well.
English ordinal numbers are almost all regular (fourth, fifth, sixth) except for a tiny irregular set at the very start (first, second, third) that you just memorize as whole words. Japanese calendar days do the same thing, but the irregular set is bigger and shows up again later in the month.
English’s irregular ordinals stop after “third,” so learners assume the pattern settles down fast. Japanese keeps irregular day-words all the way through the 10th, then brings three more back for the 14th, 20th, and 24th.
The One-Question Test: Is This One of the Special Days?
Checking before you build the word
Before attaching 日 to a number, ask: is this day the 1st–10th, 14th, 20th, or 24th? If yes, it’s a special word you memorize as a whole; if no, it’s just number + 日 (nichi).
Say you want to talk about the 4th. Run it through the test: 4 is inside the 1st–10th range, so the answer is yokka, not yon-nichi.
Now try the 15th. It falls outside the special list, so you simply build it as juugo-nichi. The test takes a second, but it saves you from the most common date mistake.
Building Months: 一月 to 十二月 and the Two Exceptions
Number plus 月, with two quiet breaks in the rule
Months are the easy part of this system. You just combine a number, one through twelve, with 月.
Three months break that pattern. 四月 is しがつ (not よんがつ), 七月 is しちがつ (not ななつき), and 九月 is くがつ (not きゅうがつ).
Japanese: 九月に京都へ旅行しませんか?
Romaji: Kugatsu ni Kyouto e ryokou shimasen ka?
English: Shall we travel to Kyoto in September?
Why: Shows the irregular month reading 九月 (kugatsu, not kyuugatsu) marked with に before the invitation-form verb 旅行しませんか (shall we…?).
Japanese: 四月に引っ越す予定です。
Romaji: Shigatsu ni hikkosu yotei desu.
English: I’m planning to move in April.
Why: Shows the irregular month reading 四月 (shigatsu, not yongatsu) combined with に before the plain-form verb 引っ越す used in the 〜予定です (planning to) construction.
Building Calendar Days: ついたち, はつか, and the Irregular Set
The words that don’t come from the regular numbers
The 1st has its own word, ついたち. It has no number root inside it at all, unlike every other date.
The 2nd through 10th each use a native Japanese reading instead of the on’yomi you would expect. Three more days break the pattern later: the 14th and 24th combine a tens-place number with the irregular word よっか, while the 20th (はつか) stands completely on its own.
Japanese: 三日は空いてる?
Romaji: Mikka wa aiteru?
English: Are you free on the 3rd?
Why: Shows the irregular calendar-day reading 三日 (mikka) in a casual question — 空いてる describes a state, so the day takes は rather than に here.
Japanese: 二十日に部屋を見に行けますか?
Romaji: Hatsuka ni heya o mi ni ikemasu ka?
English: Could we go see the room on the 20th?
Why: Shows the irregular calendar-day reading for the 20th (hatsuka) used with に before the potential-form verb 行けます.
何曜日 vs 何日: Two Questions English Squeezes Into ‘What Day’
Picking the right question word
English uses “day” for both the day of the week and the day of the month. Japanese keeps these as two separate questions.
何曜日 (nan’youbi) asks specifically for the weekday, like Monday or Tuesday. 何日 (nan-nichi) asks for the date, and the answer uses the irregular readings from the section above.
The seven weekday names come from adding 曜日 to a fixed kanji: 日曜日, 月曜日, 火曜日, 水曜日, 木曜日, 金曜日, 土曜日. This set is regular, and separate from the calendar-day readings you just learned.
Unnatural: 今日は何日ですか? (intending to ask “what day of the week is it today?”)
Natural: 今日は何曜日ですか?
English uses “day” for both the date and the weekday, so learners often default to 何日 for both meanings. Use 何曜日 for the day of the week, and save 何日 only for the date of the month.
Common Mistake: Writing 明日は四日(よんにち)です instead of 明日は四日(よっか)です. English speakers expect a date word to behave like a regular number plus suffix (four + day), so they build よん+にち instead of recalling the irregular word. Memorize the irregular calendar-day readings for the 1st–10th, plus 14th, 20th, and 24th, as whole words, not number + 日.
FAQ: Dates, Days, and Months in Japanese
How do I say dates in Japanese?
Combine the month (number + 月) and the day (number + 日) in that order, but remember the 1st–10th, 14th, 20th, and 24th use special irregular words instead of a simple number + 日.
Why is April 四月 shigatsu instead of yongatsu?
Japanese months are almost always built with the regular number readings, but 四月 and 九月 are fixed historical exceptions that use しがつ and くがつ instead of よんがつ and きゅうがつ.
What’s the difference between 何日 and 何曜日?
何日 asks for the date of the month (the 1st, the 2nd, etc.), while 何曜日 asks for the day of the week (Monday, Tuesday, etc.) — English uses “day” for both, but Japanese keeps them separate.
Quiz: Test Your Dates, Days, and Months
Try these three questions before checking the answers below.
- Fill in the blank: 明日は＿＿です (meaning “Tomorrow is the 4th”).
- How do you read 9月 out loud?
- What’s the difference in meaning between 今日は何曜日ですか? and 今日は何日ですか?
1. よっか (yokka) – Days 1-10 of the month use irregular readings, so the 4th is always よっか, never よんにち.
2. くがつ (kugatsu) – 9月 is one of the two irregular months — it’s always kugatsu, never kyuugatsu, a fixed exception you simply memorize.
3. Both are grammatically correct, but they ask for different information. – 今日は何曜日ですか? asks which day of the week it is today (e.g., Tuesday), while 今日は何日ですか? asks which date of the month it is today (e.g., the 15th) — mixing them up gets you an answer you weren’t looking for.
Summary
- Months are built simply by attaching 月 to a number, with only 四月 (shigatsu) and 九月 (kugatsu) breaking the expected pattern.
- Calendar days from the 1st to the 10th, plus the 14th, 20th, and 24th, use irregular words that must be memorized as whole units, not built from number + 日.
- 何曜日 (built from 日・月・火・水・木・金・土 + 曜日) asks for the day of the week, while 何日 asks for the date of the month, so pick the right question word for what you actually want to know.
Once these irregular words feel natural, you’re ready to practice making real plans with times attached, like asking someone to meet at a specific hour on a specific date.
