Days, Dates, and Months in Japanese (with Irregular Readings)

Dates are among the first things you say in Japanese — and among the last things you say correctly, because the system hides a cluster of irregular readings: the 1st of the month is tsuitachi (not ichinichi), the 20th is hatsuka, and 4 o'clock is yoji. This guide lays out days of the week, months, days of the month, and times — regular patterns first, traps clearly marked.

Days of the week

Each day is named for a classical element plus 曜日 (yōbi). Fully regular, endlessly useful:

Months: number + がつ

Months are simply numbered — 一月 (ichigatsu, January) through 十二月 (jūnigatsu, December). Three readings to watch, all driven by the number itself: April is しがつ (shi, not yon), July is しちがつ, September is くがつ (ku, not kyū).

Days of the month: where the irregulars live

Days 11 and up are mostly regular (じゅういちにち, じゅうごにち…), but days 1–10 use native Japanese readings, and a few special days break the pattern entirely:

Two danger pairs deserve extra reps: よっか (4th) vs ようか (8th) — one small vowel apart — and ついたち (the 1st) vs いちにち (one day's duration), same kanji 一日, different word.

Why do days 1–10 look nothing like the numbers you learned? They preserve Japan's native counting system (hi, fu, mi, yo…), which predates the Chinese-derived ichi-ni-san. You've met it before without noticing — it's the same system behind ひとつ・ふたつ・みっつ for counting objects, and behind ひとり・ふたりfor counting people. Spotting that connection turns thirteen "random" readings into one familiar pattern wearing different clothes.

Telling time

Hours are number + 時 (ji), minutes number + 分 (fun/pun). The hour irregulars echo the usual suspects: 4:00 is よじ (never yonji), 7:00 is しちじ, 9:00 is くじ (never kyūji). Minutes alternate ふん/ぷん by euphony — いっぷん, にふん, さんぷん, じゅっぷん — the same sound-change logic as the counters in our numbers and counters guide.

Relative time words: the daily vocabulary

Around the calendar system sits a set of relative words you'll use far more often than any date. They come in tidy rows — day, week, month, year — and only the day row is irregular:

Notice the pattern in the regular rows: せん〜 (last), こん〜 (this), らい〜 (next). Learn the day row as exceptions and the rest assembles itself.

Putting it together

A full date reads largest-to-smallest: 2026年6月11日（木曜日） — にせんにじゅうろくねん ろくがつ じゅういちにち もくようび. Year + 年 (nen), then month, day, weekday. No prepositions, no ordinal suffixes — just the readings.

And that's the catch: dates are pure reading-recall, the kind of knowledge that evaporates unless it's produced regularly. The fastest fix is typed repetition with randomized dates — see ３月２０日, produce sangatsu hatsuka, get checked instantly. A few sessions and ついたち/はつか stop being trivia and become reflex.