The first Japanese calendar was introduced from China, through trade with the Korean peninsula, by the Imperial Court during the Japanese Antiquity (6th century). Named koyomi or reki and written with the ideogram 暦 in Japanese, it is a lunisolar calendar based on the observation of the sun and the moon as well as their influence on nature, on animals’ behavior; and on the observation of the seasonal blooming.
Over time, the ephemeris was enriched with yearly celebrations and miscellaneous rituals aiming at attracting good fortune for all through ceremonies for abundant rice harvests for farmers, victory in battle for warriors, flourishing business for merchants and happy marriages for families. Many of these events are still celebrated and included in Shinto shrines’ yearly calendar in Japan.
The 5 sekku (節句), or dates marking the changing of seasons, are still celebrated nowadays:
September 9 (Kiku no sekku, the chrysanthemum festival).
In 1872, the Meiji Government upturned the traditional organization and officially adopted the Gregorian calendar, the solar calendar in use in Western countries. The former Japanese calendar lost its influence for the mundane but remained important in the arts and traditions. Poets largely drew inspiration from this almanac to grasp and write about the beauty of the moment in haiku.
Today, akoyomist lifestyle following the antique Japanese calendar is experiencing a revival among a population aware of environmental issues and inclined to enjoy simple things like sustainable tourism and slow life trends. Books describing the Japanese micro-seasons have been published over the past years, in many languages.
24 sekki seasonal periods and 72 kô micro-seasons
The old koyomi calendar displays a lot more seasons than the 4 main we know: spring, summer, autumn and winter. As a matter of fact:
Each of the 4 seasons is divided into 6 seasonal periods, that is to say a total of 4x6 = 24 sekki (二十四節気 nijushi sekki); then,
Each sekki is divided into 3 ko micro-seasons lasting on average 5 days each, that is to say 24x3 = 72 ko (七十二候 shichijuni kou).
The Japanese lunisolar calendar begins on February 4 for the beginning of spring, called Risshun in Japan. Every year, the exact dates can vary by 1 or 2 days depending on the position of the stars, and are fixed by the National Astronomical Observatory of Japan (NAOJ) located in Mitaka, in the west of Tokyo.
The table below summarizes the 4 seasons, divided into 24 sekkiand 72 kô, as well as the official dates of the Japanese seasons for 2025-2026.
Mountain rivers are covered by a thick layer of ice
January 25 to 29
鶏始乳
Niwatori hajimete toya ni tsuku
Hens start to lay and brood eggs
January 30 to February 3
Being the day before spring new year’s day, February 3 remains an important date for the Japanese, as the traditional Setsubun (節分) celebration. This event is called a "zassetsu", that is to say a date added in the Japanese calendar that did not exist in the original Chinese version. Setsubun used to be celebrated 4 times a year, at each changing of the annual seasons.
Flowers calendar and climate change
The 72 yearly seasons closely follow the eternal cycle of vegetation, but in reality the blooming calendar in Japan is already impacted by climate change: the World Meteorological Organization indeed announced that 2023 and 2024 were the warmest years on record.
Therefore, when traveling Japan for sakura or koyo watching, there are a few things to remember:
Every year, the blooming of cherry trees happens a few days earlier than the previous years and tends to overlap with plums and Japanese apricots (ume) blossom season. Thus, the 1rst spring blossoms can be observed as soon as early February, sometimes late January, in the warmer areas of Japan (Okinawa and Atami for example). They intensify until the end of March with a sakura flowering peak observed in the most touristic cities like Tokyo, Kyoto and Osaka. Tourists visiting Japan in April can watch cherry blossoms in the Tohoku area in the north of the capital.
The season of the red maple trees is also delayed, for example until December 10 in Tokyo, and is also shorter. The heavy summer heats indeed impact the foliage, with leaves that are drier, sometimes burnt and trees appear less leafy, especially in cities, making the koyo less impressive.
Despite seasons troubled by the changing temperatures and meteorological phenomenons, the former koyomi calendar continues to provide a delicate and poetic vision of the passing of time.
