Japanese calendar

Japanese calendar types have included a range of official and unofficial systems. At present, Japan uses the Gregorian calendar together with year designations stating the year of the reign of the current Emperor. The written form starts with the year, then the month and finally the day (meaning of the ISO 8601 standard). For example February 16, 2003 can be written 2003年2月16日. 年 reads nen and means "year", 月 reads gatsu and means "month" and finally 日 reads nichi (its pronunciation depends on the number that precedes it, see below) and means "day".
Prior to the introduction of the Gregorian calendar in 1873, the reference calendar was based on the lunisolar Chinese calendar.
History.
The lunisolar Chinese calendar was introduced to Japan via Korea in the middle of the sixth century. After that, Japan calculated its calendar using various Chinese calendar procedures, and from 1685, using Japanese variations of the Chinese procedures. But in 1873, as part of Japan's Meiji period modernization, a calendar based on the solar Gregorian calendar was introduced. In Japan today, the old Chinese calendar is virtually ignored; celebrations of the Lunar New Year are thus limited to Chinese and other Asian immigrant communities.
Japan has had more than one system for designating years. including:
Official calendar.
Years.
The official dating system known as (or, strictly speaking, ), has been in use since the late 7th century. Years are numbered within regnal eras, which are named by the reigning Emperor. Beginning with Meiji (1868–1912), each reign has been one era, but many earlier Emperors decreed a new era upon any major event; the last pre-Meiji Emperor's reign (1846–1867) was split into seven eras, one of which lasted only one year. The "nengō" system remains in wide use, especially on official documents and government forms.
The imperial year system ("kōki") was used from 1872 to the Second World War. Imperial year 1 ("Kōki" 1) was the year when the legendary Emperor Jimmu founded Japan – 660 BC according to the Gregorian Calendar. Usage of "kōki" dating can be a nationalist signal, pointing out that the history of Japan's imperial family is longer than that of Christianity, the basis of the Anno Domini (AD) system. "Kōki" 2600 (1940) was a special year. The 1940 Summer Olympics and Tokyo Expo were planned as anniversary events, but were canceled due to the Second Sino-Japanese War. The Japanese naval Zero Fighter was named after this year. After the Second World War, the United States occupied Japan, and stopped the use of "kōki" by officials. Today, "kōki" is rarely used, except in some judicial contexts.
The 1898 law determining the placement of leap years is officially based on the "kōki" years, using a formula that is effectively equivalent to that of the Gregorian calendar: if the "kōki" year number is evenly divisible by four, it is a leap year, unless the number minus 660 is evenly divisible by 100 and not by 400. Thus, for example, the year "Kōki" 2560 (AD 1900) is divisible by 4; but 2560 − 660 = 1900, which is evenly divisible by 100 and not by 400, so "kōki" 2560 was not a leap year, just as in most of the rest of the world.
The present era, Reiwa, formally began on 1 May 2019. The name of the new era was announced by the Japanese government on 1 April 2019, a month prior to Naruhito's succession to the throne. The previous era, Heisei, came to an end on 30 April 2019, after Japan's former emperor, Akihito, abdicated the throne. Reiwa is the first era name whose characters come from a Japanese root source; prior eras' names were taken from Chinese classic literature.
Seasons.
See also "Seasonal days", below.
Months.
The modern Japanese names for the months literally translate to "first month", "second month", and so on. The corresponding number is combined with the suffix ("-gatsu", "month"). The table below uses traditional numerals, but the use of Western numerals (, , etc.) is common.
In addition, every month has a traditional name, still used by some in fields such as poetry; of the twelve, "Shiwasu" is still widely used today. The opening paragraph of a letter or the greeting in a speech might borrow one of these names to convey a sense of the season. Some, such as "Yayoi" and "Satsuki", do double duty as given names (for women). These month names also appear from time to time on "jidaigeki", contemporary television shows and movies set in the Edo period or earlier.
The old Japanese calendar was an adjusted lunar calendar based on the Chinese calendar, and the year—and with it the months—started anywhere from about 3 to 7 weeks later than the modern year, so in historical contexts it is not entirely accurate to equate the first month with January.
Subdivisions of the month.
Japan uses a seven-day week, aligned with the Western calendar. The seven-day week, with names for the days corresponding to the Latin system, was brought to Japan around AD 800 with the Buddhist calendar. The system was used for astrological purposes and little else until 1876.
Just as in English the names of the days come from the Latin names (based on what the Ancient Romans considered the seven visible planets, meaning the five visible planets and the sun and the moon,) in The Far East the five visible planets are named after the five Chinese elements (metal, wood, water, fire, earth.) On the origin of the names of the days of the week, also see East Asian Seven Luminaries.
Sunday and Saturday are regarded as "Western style take-a-rest days". Since the late 19th century, Sunday has been regarded as a "full-time holiday", and Saturday a . These holidays have no religious meaning (except those who believe in Christianity or Judaism). Many Japanese retailers do not close on Saturdays or Sundays, because many office workers and their families are expected to visit the shops during the weekend. An old Imperial Japanese Navy song () says "Mon Mon Tue Wed Thu Fri Fri!" which means "We work throughout the entire week."
Japanese people also use 10-day periods called . Each month is divided into two 10-day periods and a third with the remaining 8 to 11 days:
These are frequently used to indicate approximate times, for example, "the temperatures are typical of the "jōjun" of April"; "a vote on a bill is expected during the "gejun" of this month." The magazine "Kinema Junpo" was originally published once every "jun" (i.e. three times a month).
Days of the month.
Each day of the month has a semi-systematic name. The days generally use "kun" (native Japanese) numeral readings up to ten, and thereafter "on" (Chinese-derived) readings, but there are some irregularities. The table below shows dates written with traditional numerals, but use of Arabic numerals (, , , etc.) is extremely common in everyday communication, almost the norm.
"Tsuitachi" is a worn-down form of "tsuki-tachi" (), which means "the month beginning". The last day of the month was called "tsugomori", which means "Moon hidden". This classical word comes from the tradition of the lunisolar calendar.
The 30th was also called "misoka", just as the 20th is called "hatsuka". Nowadays, the terms for the numbers 28–31 plus "nichi" are much more common. However, "misoka" is much used in contracts, etc., specifying that a payment should be made on or by the last day of the month, whatever the number is. New Year's Eve is known as , and that term is still in use.
There is traditional belief that some days are lucky ("kichijitsu") or unlucky. For example, there are some who will avoid beginning something on an unlucky day.
National holidays.
After World War II, the names of Japanese national holidays were completely changed because of the secular state principle (Article 20, The Constitution of Japan). Although many of them actually originated from Shinto, Buddhism and important events relating to the Japanese imperial family, it is not easy to understand the original meanings from the superficial and vague official names.
Notes: Single days between two national holidays are taken as a bank holiday. This applies to May 4, which is a holiday each year. When a national holiday falls on a Sunday the next day that is not a holiday (usually a Monday) is taken as a holiday.
Customary issues in modern Japan.
Gregorian months and the "One-Month Delay".
In contrast to other East Asian countries such as China, Vietnam, Korea and Mongolia, Japan has almost completely forgotten the Chinese calendar. Since 1876, January has been officially regarded as the "first month" even when setting the date of Japanese traditional folklore events (other months are the same: February as the second month, March as the third, and so on). But this system often brings a strong seasonal sense of gap since the event is 3 to 7 weeks earlier than in the traditional calendar. Modern Japanese culture has invented a kind of "compromised" way of setting dates for festivals called "Tsuki-okure" ("One-Month Delay") or "Chūreki" ("The Eclectic Calendar").
The festival is celebrated just one solar calendar month later than the date on the Gregorian calendar. For example, the Buddhist festival of Obon was the 15th day of the 7th month. Many places the religious services are held on July 15. However, in some areas, the rites are normally held on August 15, which is more seasonally close to the old calendar. (The general term "Obon holiday" always refers to the middle of August.) Although this is just de facto and customary, it is broadly used when setting the dates of many folklore events and religious festivals. But Japanese New Year is the great exception. The date of Japanese New Year is always January 1.
Seasonal days.
Some days have special names to mark the change in seasons. The 24 "sekki" () are days that divide the solar year into twenty four equal sections. is a collective term for the seasonal days other than the 24 "sekki". days are made from dividing the 24 "sekki" of a year further by three. These were named based upon the climate of Northern China, so many of the names do not fit in with the climate of Japanese archipelago. But some of these names, such as "Shunbun", "Risshū" and "Tōji", are still used quite frequently in everyday life in Japan.
The 24 sekki.
Dates can vary by one day either way.
"Zassetsu".
"Shanichi" dates can vary by as much as 5 days.
"Chūgen" has a fixed day. All other days can vary by one day.
Many "zassetsu" days occur in multiple seasons:
Seasonal festivals.
The following are known as the five seasonal festivals ( "sekku", also "gosekku"). The "sekku" were made official holidays during Edo period on Chinese lunisolar calendar. The dates of these festivals are confused nowadays; some on the Gregorian calendar, others on ""Tsuki-okure".
Not "sekku":
"Rokuyō".
The are a series of six days calculated from the date of Chinese calendar that supposedly predict whether there will be good or bad fortune during that day. The "rokuyō" are commonly found on Japanese calendars and are often used to plan weddings and funerals, though most people ignore them in ordinary life. The "rokuyō" are also known as the . In order, they are:
The "rokuyō" days are easily calculated from the Japanese lunisolar calendar. The first day of the first month is always "senshō", with the days following in the order given above until the end of the month. Thus, the 2nd day is "tomobiki", the 3rd is "senbu", and so on. The 1st day of the 2nd month restarts the sequence at "tomobiki". The 3rd month restarts at "senbu", and so on for each month. The latter six months repeat the patterns of the first six, so the 1st of the 7th is "senshō", the 1st of the 12th is "shakkō" and the moon-viewing day on the 15th of the 8th is always "butsumetsu". 
This system did not become popular in Japan until the end of the Edo period.
April 1.
The first day of April has broad significance in Japan. It marks the beginning of the government's fiscal year. Many corporations follow suit. In addition, corporations often form or merge on that date. In recent years, municipalities have preferred it for mergers. On this date, many new employees begin their jobs, and it is the start of many real-estate leases. The school year begins on April 1.