Time, dates, and days of the week: the high-frequency vocabulary worth memorizing early

Time and date vocabulary is some of the highest-return Japanese you can learn. You'll use it to catch trains, make reservations, read shop hours, and answer "what time?" a dozen times a week. The structure is mostly regular — number plus a counter — but Japanese hides a few irregular readings inside the most common spots, and those are exactly where beginners stumble.

We'll front-load the irregulars so you can't miss them, because knowing 4 o'clock is よじ and not しじ is the difference between making and missing your train.

Hours are number + 時 (ji). Most are regular — 一時 (ichiji, 1:00), 二時 (niji, 2:00) — but three break the pattern and you must learn them as exceptions:

4 o'clock = 四時 よじ (yoji), never しじ.

7 o'clock = 七時 しちじ (shichiji) — uses shichi, not nana.

9 o'clock = 九時 くじ (kuji), never きゅうじ.

For minutes, use 〜分 (fun / pun), which has its own sound changes: 一分 いっぷん (ippun), 三分 さんぷん (sanpun), 四分 よんぷん (yonpun), 十分 じゅっぷん (juppun). Half past is 〜半 (han): 二時半 (niji han — "2:30").

Add 午前 (gozen, AM) and 午後 (gogo, PM) in front: 午後三時 (gogo sanji — "3 PM"). To ask, it's 今何時ですか (ima nanji desu ka — "what time is it now?").

The days of the week all end in 曜日 (youbi) and each is named after a classical element or celestial body. This is a rare case where the logic actually helps you remember:

月曜日 (getsuyoubi, Monday — "moon"), 火曜日 (kayoubi, Tuesday — "fire"), 水曜日 (suiyoubi, Wednesday — "water"), 木曜日 (mokuyoubi, Thursday — "tree/wood"), 金曜日 (kinyoubi, Friday — "gold/metal"), 土曜日 (doyoubi, Saturday — "earth"), 日曜日 (nichiyoubi, Sunday — "sun").

The kanji 月火水木金土日 are the same characters you already meet in numbers and nature vocabulary, so this set does double duty. To ask, 何曜日ですか (nanyoubi desu ka — "what day of the week is it?").

A memory hook English speakers like: Saturday and Sunday match the West (Sun-day, and the "earth/soil" day as the weekend), and the middle five follow the same planetary logic as Romance languages — Tuesday/Mars/fire, Wednesday/Mercury/water, and so on.

Dates are where Japanese is least regular, and there's no way around memorizing. Months are easy: just number + 月 (gatsu). But like the hours, three of them shift reading:

4月 しがつ (shigatsu, April), 7月 しちがつ (shichigatsu, July), 9月 くがつ (kugatsu, September) — note these use shi/shichi/ku, the opposite choice from 4時/9時 in some cases, so check each one.

Days of the month are the hard part. The 1st through 10th, plus the 14th, 20th, and 24th, use native-Japanese readings you simply learn as words: 一日 ついたち (tsuitachi, 1st), 二日 ふつか (futsuka, 2nd), 三日 みっか (mikka, 3rd), 四日 よっか (yokka, 4th), 五日 いつか (itsuka, 5th), 六日 むいか (muika, 6th), 七日 なのか (nanoka, 7th), 八日 ようか (youka, 8th), 九日 ここのか (kokonoka, 9th), 十日 とおか (tooka, 10th).

Twenty is special: 二十日 はつか (hatsuka). From the 11th onward (except 14/20/24), it's regular: number + 日 (nichi) — 十五日 (juugonichi, 15th).

These ~13 readings are the single biggest memorization chunk in this article. Drill them like vocabulary, because "the 20th" comes up constantly and はつか sounds nothing like the number twenty.

Often you don't need a calendar date at all — you need "tomorrow" or "next week". These high-frequency words deserve a spot on your first flashcard deck:

Days: 今日 (kyou, today), 明日 (ashita, tomorrow), 昨日 (kinou, yesterday), 明後日 (asatte, day after tomorrow), 一昨日 (ototoi, day before yesterday).

Weeks: 今週 (konshuu, this week), 来週 (raishuu, next week), 先週 (senshuu, last week).

Months: 今月 (kongetsu, this month), 来月 (raigetsu, next month), 先月 (sengetsu, last month).

Notice the pattern: 今 (kon/this) for the current period, 来 (rai/coming) for next, 先 (sen/previous) for last. Learn that trio and 来週/来月/来年 (next year) all click at once.

Put it together and you can handle most scheduling: 来週の金曜日、午後三時はどうですか (raishuu no kinyoubi, gogo sanji wa dou desu ka — "how about 3 PM next Friday?"). That one sentence is most of what booking anything requires.