Koyomi Days

Koyomi Days is a free reference site for East Asian calendars, seasonal markers, and the I Ching. It brings date lookup, calendar notes, and classical text reference into a browser, with tools adapted to local calendar conventions. The Japanese pages include rokuyo, Ichiryumanbaibi, and yearly calendar lists. The English pages include an I Ching reference and interactive hexagram tools. Traditional Chinese pages provide lunar calendar lookup and solar terms. The site supports 17 languages; the available tools differ by locale. Results follow defined calculation rules. Method pages explain the rules and cite sources, while reference pages distinguish classical text from translation and commentary. These details let readers inspect how a result was obtained. No account is required, and the site currently shows no ads. Once the relevant page and scripts have loaded, calculations run locally and can continue offline. Opening other pages or loading additional text still requires a connection. Koyomi Days works on desktop and mobile browsers and remains a separate product from its recommended app, Koyonari.