Chinese Perpetual Calendar (萬年曆)

The Chinese Perpetual Calendar (萬年曆): A Browsable Lunisolar Almanac

A 萬年曆 ("ten-thousand-year calendar") does not literally span ten thousand years — the phrase is a Chinese idiom for a general-purpose almanac you can page through to look up any year and month. Unlike a single-date converter, it lays a whole month out as a grid so you can see, at a glance, every day's Gregorian date, its lunar date, which days are solar terms, and which fall on traditional festivals. This tool reproduces exactly that form: it opens on the current month, lets you flip with ◀ / ▶ or jump anywhere with the Year and Month dropdowns, and covers the two centuries from 1901 to 2100, the span of the Hong Kong Observatory's Gregorian-Lunar conversion tables, against which every day here has been checked. Every calculation runs locally in your browser — no network calls, no model.

What makes a perpetual calendar so useful is that it shows "the calendar of the sun" and "the calendar of the moon" side by side. The Gregorian calendar is purely solar, so its dates line up with the seasons. The Chinese lunar calendar is lunisolar: its months follow the phases of the moon, while leap months and the 24 solar terms quietly pull the sun's pace back into step. When a cell shows the lunar month name on 初一 (the first lunar day, e.g. 五月 "fifth month"), you are literally seeing a new moon — the first day of each lunar month is the day of the new moon. Stacking both systems on one grid makes it intuitive why Chinese New Year, Dragon Boat, and Mid-Autumn land on different Gregorian dates each year, and lets you answer questions like "when is Qingming next year?" in a glance.

Solar terms, festivals, and the daily almanac

This calendar embeds two kinds of marker into each cell. Green tags are the 24 solar terms — Start of Spring, Spring Equinox, Summer Solstice, White Dew, Winter Solstice and so on. These are fixed points on Earth's orbit around the sun, the genuinely astronomical component of the lunar calendar, and there are exactly 24 of them a year. Red tags are traditional festivals such as Chinese New Year, Lantern, Dragon Boat, Qixi, Ghost Festival, Mid-Autumn, Double Ninth, and Winter Solstice, whose dates are fixed by the lunar calendar. Tap any day and the detail panel expands that day's complete 老黃曆: year and day stem-branch, zodiac, 宜 (activities to do), 忌 (activities to avoid), the day's clashing zodiac sign and inauspicious direction, the 建除 twelve day-officers, the 廿八宿 lunar mansion with its luck reading, the fetus-spirit position, and the day and year nine-star. The 建除 officers, the 廿八宿 mansions and the clash directions all appear in the Qing court's 《欽定協紀辨方書》; the 宜/忌 tables this page uses come from the open-source 6tail library and have not been checked against that book entry by entry.

"To harmonise the reckoning and distinguish the directions is to revere heaven's order and earth's quarters." Qianlong Emperor, preface to the 欽定協紀辨方書 (1741–42), Wikisource, Siku Quanshu text (our translation of 「協紀辨方者,敬天之紀,敬地之方也」)

Cultural stance + disclaimer

A perpetual calendar is a calendrical tool, and its most reliable parts — Gregorian dates, lunar conversion, the 24 solar terms, zodiac and stem-branch — are computed from astronomical formulae and checked day by day against the Hong Kong Observatory's tables: of 73,049 days from 1901 to 2100 only the 30 days of the fourth lunar month of 1906 differ, because its new moon fell 7 minutes 49 seconds before midnight. You can rely on them for checking festivals, cross-referencing birthdays and planning trips. But the 宜忌 and 神煞 you see after tapping a day are a different matter: they are folk tradition with no scientific basis, and different almanacs routinely disagree on the same day's do-and-avoid lists. This tool uses an embedded open-source 通書 algorithm (the 6tail implementation), so its output may differ slightly from a paper almanac on your shelf — that is normal, because date-selection has many competing schools and no single authoritative answer. Treat the calendar as a handy calendrical reference and cultural cross-check; for real-life milestones — weddings, business openings, moving house — rely on practical conditions, professional advice, and family coordination rather than any single day's 宜忌. RECATOOLS applies zero-tracking and zero-storage to every date you enter: all computation stays on your own device.