This is an overview of the names and the etymology of Japanese weekdays and the days of the month.

English WeekdayJapanese WeekdayMeaning
Monday月曜日 getsuyōbiThe Day of the Moon, 月 (tsuki, the moon)
Tuesday火曜日 kayōbiThe Day of Fire, 火 (ka, fire), refers to the planet Mars (火星 kasei)
Wednesday水曜日 suiyōbiThe Day of Water, 水 (mizu, water), refers to the planet Mercury (水星 suisei)
Thursday木曜日 mokuyōbiThe Day of Wood, 木 (ki, tree or wood), refers to the planet Jupiter (木星 mokusei)
Friday金曜日 kinyōbiThe Day of Metal, 金 (kin, metal or gold), refers to the planet Venus (金星 kinsei)
Saturday土曜日 doyōbiThe Day of Earth, 土 (do, earth or soil), refers to the planet Saturn (土星 dosei)
Sunday日曜日 nichiyōbiThe Day of the Sun, 日 (hi, sun), refers to the Sun (also 太陽 taiyō)

Days of the month


Until the 1870s, the Japanese used an adjusted lunar calendar based on the Chinese calendar and without weeks. The old Japanese calendar just counted the days of each month.

1一日tsuitachi
("ippi" is also in legal or business use)
17十七日jūshichinichi
2二日futsuka18十八日jūhachinichi
3三日mikka19十九日jūkunichi
4四日yokka20二十日hatsuka
5五日itsuka21二十一日nijūichinichi
6六日muika22二十二日nijūninichi
7七日nanoka23二十三日nijūsannichi
8八日yōka24二十四日nijūyokka
9九日kokonoka25二十五日nijūgonichi
10十日tōka26二十六日nijūrokunichi
11十一日jūichinichi27二十七日nijūshichinichi
12十二日jūninichi28二十八日nijūhachinichi
13十三日jūsannichi29二十九日nijūkunichi
14十四日jūyokka30三十日sanjūnichi
15十五日jūgonichi31三十一日sanjūichinichi
16十六日jūrokunichi---


Adoption of the Western calendar


With the introduction of the Western calendar, names for the seven days of the week were adopted as well. They were partly derived from the Latin system. The Romans used the names of the seven planets of classical astronomy and numbered the days, beginning with Sunday. The East Asian naming system of weekdays is quite similar the Latin system and is based on the “Seven Luminaries” (七曜 shichiyō), which consists of the Sun, Moon and the five planets visible to the naked eye.

The five planets are named after the five elements in traditional East Asian philosophy: Fire (Mars), Water (Mercury), Wood (Jupiter), Metal (Venus), and Earth (Saturn). The Chinese transliteration of the planetary system was soon brought to Japan by the Japanese monk Kobo Daishi (弘法大師). Diaries of the Japanese statesman Fujiwara no Michinaga (藤原道長) show the seven-day system in use during the Heian Period. It was kept in use for astrological purposes until its promotion to a Western-style calendar during the Meiji era.