How Rokuyō, Ichiryū Manbaibi and Tenshabi Are Determined

Almanac notes are custom, not science

Rekichū, or almanac notes, are lucky and unlucky labels attached to calendar dates. They include the six-day rokuyō cycle and selected days such as ichiryū manbaibi, tenshabi and fujōjubi. Since the Meiji-era calendar reform they have not appeared in official calendars, but they live on in commercial ones.

Every label is assigned mechanically from the lunisolar calendar or the sexagenary day cycle, and none has been shown to affect events. Still, they shape wedding bookings and funeral dates in Japan, so understanding them helps you respect others' preferences without being ruled by them.

The old lunisolar calendar

The traditional Japanese calendar starts each month on the day of the new moon, giving months of 29 or 30 days. Twelve such months are about 11 days shorter than a solar year, so months are named by which of the solar "principal terms" (such as the equinoxes) they contain. A month with no principal term becomes a leap month, which happens roughly once every three years.

Because a month begins on the calendar date of the new moon, the result depends on the time zone. Japan uses Japan time. The ninth lunar month of 2026 begins on October 11 in Japan but on October 10 in the Chinese calendar, because the new moon falls just after midnight in Japan but before midnight in China (UTC+8).

Rokuyō: lunar month plus day, divided by six

The six rokuyō days are sensho, tomobiki, senbu, butsumetsu, taian and shakkō. Add the lunar month and day and divide by 6: a remainder of 0 is taian, 1 shakkō, 2 sensho, 3 tomobiki, 4 senbu and 5 butsumetsu. So the first day of each lunar month always has the same label: months 1 and 7 start with sensho, 2 and 8 with tomobiki, 3 and 9 with senbu, 4 and 10 with butsumetsu, 5 and 11 with taian, and 6 and 12 with shakkō.

Within a month the labels cycle in order, but they jump when a new lunar month starts. In 2026, February 17 (lunar new year) is sensho and March 19 (start of the second month) is tomobiki. November 8 (ninth month, day 29) is sensho, and November 9 starts the tenth month, so it is butsumetsu, skipping two labels. Taian is considered lucky all day and butsumetsu unlucky; many crematoria close on tomobiki because funerals are avoided that day.

Ichiryū manbaibi: solar month and zodiac day

Ichiryū manbaibi, "the day one grain becomes ten thousand," is considered good for starting things. It uses solar months that begin at each of the 12 solar "sectional terms" (such as the start of spring around February 4), together with the zodiac animal assigned to each day in a 12-day cycle. Each solar month has two animals; for example, the tiger month from the start of spring uses ox and horse days.

This gives 4 to 7 days per calendar month and 64 days in 2026. You can see the solar month change in November 2026: before the start of winter on November 7, horse days qualify, so November 4 is one; from November 7, rooster and dog days qualify, so November 7 and 8 are. Almanacs do not all use the same table, so dates can differ between sources.

Tenshabi and fujōjubi

Tenshabi, often called the luckiest day of the year, is a specific sexagenary day in each season: tsuchinoe-tora in spring, kinoe-uma in summer, tsuchinoe-saru in autumn and kinoe-ne in winter, with seasons defined by solar months. The 60-day cycle meets each roughly 90-day season once or twice, so there are only five or six per year. In 2026 they fall on March 5, May 4, May 20, July 19, October 1 and December 16.

Fujōjubi, days when nothing is said to succeed, come every eight days from a starting date fixed for each lunar month (day 3 in months 1 and 7, for example). Because each label follows its own independent rule, they can collide: May 20 and July 19, 2026 are both tenshabi and fujōjubi. That alone shows the system was never designed to be consistent.

• Rokuyō: (lunar month + lunar day) mod 6
• Ichiryū manbaibi: two zodiac days per solar month
• Tenshabi: one sexagenary day per season
• Fujōjubi: every eight days from a fixed lunar-month start

Using them sensibly

How much weight to give these labels varies by region, family and industry. A practical approach is to treat them as one consideration for the people involved, alongside venue availability, schedules and cost.