Time, Date, and Calendar Vocabulary in Japanese

Japanese time, date, and calendar vocabulary is the N5 word set that covers four areas at once: days of the week, months, the clock counters 時/分/秒 (hours, minutes, seconds), and relative-time words such as 今日 (today) and 明日 (tomorrow).¹² Most of it is regular. The days of the month, however, have deliberately preserved irregular readings, and learners often need those spelled out in one place.³

Overview

Two things make this vocabulary harder than a plain word list. First, Japanese time words draw on two different number systems. The same digit can read more than one way depending on the counter it joins.⁴³ Second, the calendar dates from the 1st to the 10th break the regular pattern because they preserve an older native counting system.³

Knowing which system a word belongs to turns the set from rote memorisation into something predictable. Month names and the hour, minute, and second counters follow regular Sino-Japanese patterns. The day-of-month readings 1–10 do not.⁵²

How Japanese time words are built

Japanese has two parallel number series. The Sino-Japanese series (kango, borrowed from Chinese: いち, に, さん…) drives the regular, productive counters.⁴ The native-Japanese series (wago, inherited: ひと(つ), ふた(つ), みっ(つ)…) survives in a handful of irregular forms.³

Sino-Japanese numbers build the month names (number + 月 がつ), the hours (number + 時 じ), the minutes (number + 分 ふん/ぷん), the seconds (number + 秒 びょう), and the dates from the 11th onward (number + 日 にち).⁵² Native-Japanese counting remains in the irregular dates. The 2nd through the 10th (plus the 14th and 24th) take a wago number root plus the day suffix か, and the 20th is はつか.³⁶

The day-of-week names sit on a third, older layer: the seven luminaries (七曜). This system pairs each of the five Chinese elements, plus the sun and the moon, with a celestial body.⁴

Why one kanji reads two ways in time contexts

The two-system split is why 一日 reads ついたち for the 1st of the month (a whole-word reading), but いちにち for "one day" in general.⁷ Likewise, 四月 is しがつ (April), while 四日 is よっか (the 4th).³

Register: casual vs. formal/Sino-Japanese pairs

Several relative-time words have a casual native reading and a formal Sino-Japanese reading written with the same kanji. 明日 (tomorrow) is casual あした, neutral あす, or formal みょうにち in business letters and announcements.⁸ 昨日 (yesterday) is casual きのう or formal さくじつ in news and formal writing.⁹ 一昨日 (the day before yesterday) is casual おととい or formal いっさくじつ.³

The casual reading is the everyday default in speech; the Sino-Japanese reading surfaces in news broadcasts, business correspondence, and formal writing.⁸⁹

明日あしたテストがあります。²
"There is a test tomorrow."

昨日きのうは休やすみでした。²
"Yesterday was a day off."

Days of the week

The seven weekday words (月曜日–日曜日)

Each weekday is a luminary kanji + 曜日 (ようび). 曜 means "shining body" or "luminary." The set is the 七曜 (seven luminaries) of classical Chinese astronomy. It was transmitted to Japan through Buddhist astrological texts associated with 空海 (Kūkai) in the early 9th century.⁴³

Day	Kanji	Reading	Romaji	Luminary / element	Planet
Monday	月曜日	げつようび	getsuyōbi	月 moon	Moon4
Tuesday	火曜日	かようび	kayōbi	火 fire	Mars4
Wednesday	水曜日	すいようび	suiyōbi	水 water	Mercury4
Thursday	木曜日	もくようび	mokuyōbi	木 wood	Jupiter4
Friday	金曜日	きんようび	kin'yōbi	金 metal/gold	Venus4
Saturday	土曜日	どようび	doyōbi	土 earth	Saturn4
Sunday	日曜日	にちようび	nichiyōbi	日 sun	Sun4

The element-to-planet pairing follows the Chinese five-elements system: 火 fire is Mars, 水 water is Mercury, 木 wood is Jupiter, 金 metal is Venus, and 土 earth is Saturn.⁴

今日きょうは水曜日すいようびです。²
"Today is Wednesday."

Asking and saying "what day" (何曜日)

"What day of the week?" is 何曜日 (なんようび).² In casual speech, the 日 can drop, leaving 〜曜 (げつよう, かよう…). The full 〜曜日 is the neutral default.⁴

今日きょうは何曜日なんようびですか。²
"What day of the week is it today?"

Months

The twelve month names (1月–12月)

A month name is a Sino-Japanese number + 月 (がつ).² Three readings break the simple pattern because the numbers take their Sino reading rather than their common alternates. They are 4月 しがつ (not よん), 7月 しちがつ (not なな), and 9月 くがつ (not きゅう).²

Month	Kanji	Reading	Romaji
January	一月	いちがつ	ichigatsu2
February	二月	にがつ	nigatsu2
March	三月	さんがつ	sangatsu2
April	四月	しがつ	shigatsu2
May	五月	ごがつ	gogatsu2
June	六月	ろくがつ	rokugatsu2
July	七月	しちがつ	shichigatsu2
August	八月	はちがつ	hachigatsu2
September	九月	くがつ	kugatsu2
October	十月	じゅうがつ	jūgatsu2
November	十一月	じゅういちがつ	jūichigatsu2
December	十二月	じゅうにがつ	jūnigatsu2

誕生日たんじょうびは四月しがつです。²
"My birthday is in April."

月 as month-name vs. ヶ月 as month-count

〜月 (がつ) names a calendar month: 四月 is April.² 〜か月 / 〜ヶ月 (かげつ) is a duration counter for a span of months. It uses Sino numbers: 四か月 (よんかげつ) is "four months long."²

The same digit therefore reads differently by function: 四月 しがつ (April) but 四か月 よんかげつ (four months); 七月 しちがつ (July) but 七か月 ななかげつ (seven months).²

The small ヶ in ヶ月 is not read "ke"

The ヶ in 〜ヶ月 is a written abbreviation, not a katakana sound. The whole counter is read かげつ.²

日本にほんに三さんか月げついます。²
"I will be in Japan for three months."

Telling the time: hours, minutes, seconds

Hours (時)

An hour is a Sino number + 時 (じ).⁵² Three irregular readings parallel the month traps. They are 4時 よじ (not し or よん), 7時 しちじ, and 9時 くじ.⁵²

For the day's halves, 午前 (ごぜん) is a.m. and 午後 (ごご) is p.m. 半 (はん) after the hour means "half past," that is, :30.²

Hour	Kanji	Reading	Romaji
1	一時	いちじ	ichiji5
2	二時	にじ	niji5
3	三時	さんじ	sanji5
4	四時	よじ	yoji5
5	五時	ごじ	goji5
6	六時	ろくじ	rokuji5
7	七時	しちじ	shichiji5
8	八時	はちじ	hachiji5
9	九時	くじ	kuji5
10	十時	じゅうじ	jūji5
11	十一時	じゅういちじ	jūichiji5
12	十二時	じゅうにじ	jūniji5

今いま、四時半よじはんです。²
"It's four thirty now."

Minutes (分) and seconds (秒)

A minute is a Sino number + 分, read ふん or ぷん by a euphonic sound rule, a sound change that makes the word easier to pronounce.⁵ The ぷん reading follows 1, 3, 4, 6, 8, and 10, and the number itself may also change: 一分 いっぷん, 三分 さんぷん, 四分 よんぷん, 六分 ろっぷん, 八分 はっぷん, 十分 じゅっぷん.⁵ The plain ふん reading follows 2, 5, 7, and 9: 二分 にふん, 五分 ごふん, 七分 ななふん, 九分 きゅうふん.⁵

Seconds are regular: 秒 (びょう), as in 三十秒 (さんじゅうびょう).⁵

Minute	Kanji	Reading	Romaji
1	一分	いっぷん	ippun5
2	二分	にふん	nifun5
3	三分	さんぷん	sanpun5
4	四分	よんぷん	yonpun5
5	五分	ごふん	gofun5
6	六分	ろっぷん	roppun5
7	七分	ななふん	nanafun5
8	八分	はっぷん	happun5
9	九分	きゅうふん	kyūfun5
10	十分	じゅっぷん / じっぷん	juppun / jippun5

五分ごふん待まってください。²
"Please wait five minutes."

Two accepted readings for 十分

十分 is read じゅっぷん in everyday speech, while じっぷん is the historically prescribed reading still listed in some dictionaries and broadcast standards.⁵

Dates: days of the month

The pattern from the 11th on (number + にち)

From the 11th onward, dates are regular: a Sino number + 日 (にち). Examples include 十一日 じゅういちにち, 十五日 じゅうごにち, 二十五日 にじゅうごにち, and 三十一日 さんじゅういちにち.³

Only three dates in this range break the pattern: the 14th, the 24th, and the special 20th covered below. The 14th and 24th do so because they contain 4.³

The irregular days 1–10, plus 14, 20, 24

Days 1 through 10 use native (wago) counting plus the day suffix か. The one exception is the 1st, which has the whole-word reading ついたち.³⁷

Date	Kanji	Reading	Romaji	Note
1st	一日	ついたち	tsuitachi	jukujikun, not いちにち7
2nd	二日	ふつか	futsuka	wago ふた + か3
3rd	三日	みっか	mikka	wago み + か3
4th	四日	よっか	yokka	wago よ + か3
5th	五日	いつか	itsuka	wago いつ + か3
6th	六日	むいか	muika	wago む + か3
7th	七日	なのか	nanoka	wago なの + か3
8th	八日	ようか	yōka	wago よう + か3
9th	九日	ここのか	kokonoka	wago ここの + か3
10th	十日	とおか	tōka	wago とお + か3
14th	十四日	じゅうよっか	jūyokka	embedded よっか3
20th	二十日	はつか	hatsuka	special wago form6
24th	二十四日	にじゅうよっか	nijūyokka	embedded よっか3

All other dates (11, 12, 13, 15–19, 21, 22, 23, 25–31) take the regular にち reading.³

三日みっかに会あいましょう。²
"Let's meet on the 3rd."

今日きょうは二十日はつかです。²
"Today is the 20th."

Where the irregular readings come from

ついたち (1st) is a jukujikun, a reading assigned to the whole compound. It comes from 月立ち (つきたち), "the moon rises" or "the month begins." This referred to the new moon that opened each month in the old lunisolar calendar. Over time, つきたち contracted to ついたち.⁷

ふつか, みっか, よっか… preserve the native counting roots ふた (2), み (3), よ (4), いつ (5), む (6), なの (7), よう (8), ここの (9), and とお (10), each fused with the day suffix か.³ はつか (20th) comes from the native "twenty" root. 二十 (はた) shifted to はつ and joined the day suffix か, with an older form はたか also linked to はたち, "twenty years old."⁶

The day suffix か is the same native element running across 二日 to 十日. It is historically distinct from the Sino にち reading that takes over from the 11th.³

Relative time words

Day axis (おととい–あさって)

The day axis runs from two days back to two days forward, each with a fixed word.

Word	Kanji	Reading	Romaji	Meaning
day before yesterday	一昨日	おととい	ototoi	-2 days3
yesterday	昨日	きのう	kinō	-1 day9
today	今日	きょう	kyō	02
tomorrow	明日	あした	ashita	+1 day8
day after tomorrow	明後日	あさって	asatte	+2 days2

The same kanji also have formal Sino-Japanese readings: 昨日 さくじつ, 明日 みょうにち (with neutral あす alongside), and 一昨日 いっさくじつ.⁹⁸

明後日あさって、京都きょうとへ行いきます。²
"I'm going to Kyoto the day after tomorrow."

Week, month, and year axes

A regular 先〜・今〜・来〜 prefix grid creates the words for "last," "this," and "next" across week, month, and year.²

Axis	last	this	next
week (週)	先週 せんしゅう	今週 こんしゅう	来週 らいしゅう2
month (月)	先月 せんげつ	今月 こんげつ	来月 らいげつ2
year (年)	去年 きょねん	今年 ことし	来年 らいねん2

The year row breaks the prefix pattern: "last year" is 去年 (きょねん), not 先年, and "this year" is the native reading 今年 (ことし).²

来週らいしゅう、試験しけんがあります。²
"There is an exam next week."

Nuance and usage contexts

When time words take に and when they don't

Absolute time expressions (clock times, dates, month names, days of the week) take the particle に: 三時に, 四日に, 月曜日に.² Relative time words (今日, 明日, 昨日, 毎日, 来週, 今年…) normally do not take に. They stand bare as adverbs.²

七時しちじに起おきます。²
"I get up at seven."

明日あした来きます。²
"I'll come tomorrow."

Over-applying に to relative-time words

Adding に to a relative word is among the most common beginner errors: 明日に行きます is wrong. Relative words like 今日 and 明日 stand bare, so the correct form is 明日行きます.²

Casual vs. formal/written equivalents

The register pairs from the day axis line up cleanly. Each casual spoken form has a Sino-Japanese counterpart for writing.

Casual (speech)	Formal / written	Meaning
きのう (昨日)	さくじつ (昨日)	yesterday9
あした (明日)	みょうにち (明日) / あす	tomorrow8
おととい (一昨日)	いっさくじつ (一昨日)	day before yesterday3

The casual readings dominate everyday conversation; the Sino-Japanese readings appear in news broadcasts, public announcements, and business correspondence.⁸⁹

Good to know

The 4 / 7 / 9 reading trap across all four domains

The numbers 4, 7, and 9 each have both a Sino and a native reading. Japanese picks whichever one the fixed counter idiom demands. There is no single rule, so each combination is learned as a set.⁵²

For 4, し appears in 四月 (April); よ in 四時 よじ (4 o'clock) and 四日 よっか (the 4th); and よん in 四分 よんぷん and 四か月 よんかげつ.⁵² For 7, しち appears in 七月 (July) and 七時 (7 o'clock); なな in 七分 ななふん; and the wago root なの in 七日 なのか.⁵² For 9, く appears in 九月 (September) and 九時 (9 o'clock); きゅう appears in 九分 きゅうふん.⁵²

Why ついたち never means "one day"

一日 is a jukujikun with two readings split by meaning, so the calendar sense and the duration sense are read differently. For "the 1st of the month," 一日 is read ついたち, from 月立ち. いちにち means "one day" or "a whole day."⁷

Reading 一日 as いちにち when the calendar date is meant is a frequent comprehension trap. The correct calendar form is the whole-word reading:

一日ついたち
"the 1st of the month"

Mnemonics for the irregular dates

The days of the month from 2 to 10 are not random. ふつか, みっか, よっか… are the native object-counters ふたつ, みっつ, よっつ with their tails swapped for か. That makes the native-counting series the memory hook.³ Learning one row gives most of the date irregulars at once.³

ついたち as "the moon stands up"

ついたち comes from 月立ち (つきたち): the new moon that began each lunisolar month. The form contracted over time to ついたち. Knowing the origin explains both the odd reading and why it means specifically the 1st.⁷

半 for :30, and minutes are otherwise just counted

〜時半 (はん) means "half past," so 三時半 is 3:30.² There is no native idiom for "quarter past." "x:15" is simply 十五分 (じゅうごふん), and "x:45" is 四十五分.² 半 is the only special fraction word in clock time. Every other minute value uses the plain 分 counter.²

See also

• Adverbial Forms of Japanese Adjectives: く and に
• Japanese Weather and Seasons Vocabulary: 天気, 四季, and the 降る/吹く Verbs
• Japanese Money and Shopping Vocabulary: 円, 買う/売る/払う, and いくらですか
• How to Learn Japanese Vocabulary: A Strategy by Level
• Word Frequency in Japanese: Why the First 1,000 Words Cover ~80%

References

Footnotes

1. 国際交流基金・日本国際教育支援協会 (Japan Foundation & Japan Educational Exchanges and Services). JLPT Japanese-Language Proficiency Test — official site. https://www.jlpt.jp/e/ — level structure and the long-standing inclusion of basic time/date/calendar vocabulary in the N5 lexical scope. The JLPT does not publish an official word list; N5 placement of this set follows standard N5 curricula consistent with the official can-do statements. ↩

2. Banno, Eri, et al. Genki I: An Integrated Course in Elementary Japanese. 3rd ed., The Japan Times, 2020. — standard elementary textbook treatment of clock time (〜時, 〜分, 半, 午前/午後), days of the week, dates, and relative-time words; basis for register and the に-particle usage pattern. (General textbook reference; specific page numbers not pinned in this pass — see Open issues.) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹ ↩³⁰ ↩³¹ ↩³² ↩³³ ↩³⁴ ↩³⁵ ↩³⁶ ↩³⁷ ↩³⁸ ↩³⁹ ↩⁴⁰ ↩⁴¹ ↩⁴² ↩⁴³ ↩⁴⁴ ↩⁴⁵ ↩⁴⁶ ↩⁴⁷ ↩⁴⁸ ↩⁴⁹ ↩⁵⁰ ↩⁵¹ ↩⁵² ↩⁵³ ↩⁵⁴ ↩⁵⁵ ↩⁵⁶

3. sci.lang.japan FAQ (Ben Bullock, ed.). "Where did the Japanese get their names for the weekdays?" / "What are the Japanese days of the month?" https://www.sljfaq.org/afaq/days-of-week.html and https://www.sljfaq.org/afaq/month-days.html — weekday transmission via 空海 (Kūkai / Kōbō Daishi) and the day-of-month native-counting readings. (limitation) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹

4. Bauer, Robert (CJVlang). "Japanese Days of the Week: The 'Seven Luminaries'." cjvlang.com. http://www.cjvlang.com/Dow/dowjpn.html — the 七曜 (seven luminaries) system, the five-elements/planet equations (火=Mars, 水=Mercury, 木=Jupiter, 金=Venus, 土=Saturn), and the transmission history into Japan. (limitation) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³

5. The Japan Foundation, Japanese-Language Institute, Kansai. "じかん 時間 (Time)," Nihongo de Care-Navi counting/time reference. https://eng.nihongodecarenavi.jp/pdf/count_time.pdf — pedagogy reference for hour (時) and minute (分) readings and the ふん/ぷん euphonic split. (PDF; content known from publisher description, binary not machine-extracted in this pass — see Open issues.) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹ ↩³⁰ ↩³¹ ↩³² ↩³³ ↩³⁴ ↩³⁵

6. Wiktionary contributors. "二十日." Wiktionary, the free dictionary. https://en.wiktionary.org/wiki/二十日 — etymology of はつか: 二十 (はた) apophonic to はつ + day suffix 日 (か); alternative derivation from はたち + か. (limitation) ↩ ↩² ↩³

7. Wiktionary contributors. "一日." Wiktionary, the free dictionary. https://en.wiktionary.org/wiki/一日 — etymology entry citing the derivation of ついたち from 月 (tsuki) + 立ち (tachi). Wiktionary aggregates and cites Japanese dictionary sources (日本国語大辞典, 大辞林); treated here as a tertiary reference for etymology. (limitation) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

8. Wiktionary contributors. "明日." Wiktionary, the free dictionary. https://en.wiktionary.org/wiki/明日 — readings あした / あす / みょうにち and their register stratification. (limitation) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

9. Wiktionary contributors. "昨日." Wiktionary, the free dictionary. https://en.wiktionary.org/wiki/昨日 — readings きのう / さくじつ and register stratification. (limitation) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶