Koyomi (暦)

The Almanac of Auspicious Days

Overview

Koyomi is the traditional Japanese almanac, a layered calendar that tells you not only the date but the quality of each day. Its best-known feature is the Rokuyō, a repeating six-day cycle, Sensho, Tomobiki, Senbu, Butsumetsu, Taian, and Shakkō, that ranks days from highly auspicious to inauspicious. Around it sit the twenty-four sekki seasonal markers tracking the solar year, plus selected lucky and unlucky days for specific acts. Even today the koyomi shapes when Japanese couples marry, when funerals are scheduled, and when businesses launch. Because it draws on shared cultural convention rather than paid computation, this endpoint is free.

Origin & history

Japan adopted the Chinese lunisolar calendar via Korea in the sixth and seventh centuries, with the Genka calendar reportedly transmitted around 604 CE. The Rokuyō cycle itself arrived later, traced to Chinese reckoning and popularized in Japan from the late Kamakura and Muromachi periods, gradually attaching the day-quality labels still printed in almanacs today.

For centuries the imperial court and later the Tokugawa shogunate controlled calendar production; the astronomer Shibukawa Harumi (1639–1715) created the Jōkyō calendar of 1685, the first based on native Japanese observation. After Japan switched to the Gregorian calendar in 1873, the old almanac persisted as the kyūreki, and the Rokuyō survived into modern diaries, wedding planners, and smartphone apps as a living guide to auspicious timing.

How it works

The koyomi assigns each day a Rokuyō label whose fortunes shift by the hour: Taian is wholly lucky, Butsumetsu wholly unlucky, while Sensho favors mornings and Senbu favors afternoons, and Tomobiki is shunned for funerals. Overlaid are the sekki, twenty-four solar terms like Risshun and Geshi that mark seasonal turns, alongside other selected auspicious and inauspicious days. Together they answer when to act and when to wait. The askTIAN API returns the date’s Rokuyō, its auspiciousness, the current sekki, and notes on favorable activities.

Good for

Use cases

Wedding Day Check

Confirm whether a chosen date falls on Taian, the most auspicious Rokuyō for marriages and celebrations.

Launch Timing

Pick a favorable day to open a business, sign a contract, or begin a venture by reading the day’s grade.

Funeral Scheduling

Avoid Tomobiki, traditionally shunned for funerals because the name implies pulling friends toward death.

Seasonal Tracking

Follow the twenty-four sekki to align activities and intentions with the turning of the solar year.

Key terms

Rokuyō
The six-day cycle (Taian, Butsumetsu, Sensho, Tomobiki, Senbu, Shakkō) ranking each day’s overall fortune.
Taian
The most auspicious Rokuyō day, favored for weddings, openings, and any important undertaking.
Sekki
The twenty-four solar terms dividing the year into seasonal segments such as Risshun and Geshi.
Kyūreki
The old lunisolar calendar retained after 1873 alongside the official Gregorian system.

API

The askTIAN Koyomi API returns the date’s Rokuyō label, its auspiciousness, the active sekki, recommended activities, and a 0–100 score at no cost.

Endpoint: POST /trpc/japanese.koyomi — 0 TIAN Points. See the API documentation and Playground.