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Chinese Perpetual Calendar

Three calendars are in simultaneous use in Chinese contexts: the Gregorian calendar, the lunisolar calendar, and the solar-term calendar. Their years and months begin at different points, and mixing them is the root of most date conversion errors.

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The Chinese calendar is lunisolar, not lunar

It is commonly called a lunar calendar, but it is lunisolar. Months follow the synodic month, so the first day of a month always falls on a new moon and a month is twenty-nine or thirty days. Years must still track the tropical year, which is handled by inserting leap months.

The insertion rule is defined by the twelve major solar terms: a month that contains none of them becomes a leap repetition of the preceding month. This determines exactly which year and which month receive a leap, and is not an arbitrary adjustment.

The solar-term calendar is bounded by terms

The solar-term calendar is purely solar. Its year begins at Start of Spring and its months at twelve of the solar terms, with no relation to the first day of a lunar month. BaZi, Qi Men and related systems all use this calendar.

This is why the question of when the zodiac year changes has two answers. By the lunisolar calendar it changes at the lunar new year; by the solar-term calendar it changes at Start of Spring. The two disagree for the period between them.

The twenty-four solar terms

Solar terms divide the ecliptic into equal fifteen-degree arcs. Because they are defined by the position of the sun, their Gregorian dates are highly stable, usually varying by only a day or two, while their lunisolar dates drift considerably.

The terms alternate between two kinds. Twelve of them bound the months of the solar-term calendar; the other twelve are the major terms used to decide leap months. The two sets serve different purposes and are not interchangeable.

The twenty-four solar terms in 2026

How to use it

  1. Pick a Gregorian date to see the lunisolar date and the sexagenary stem and branch
  2. Check the exact times of this year the twenty-four solar terms
  3. Move to the date selection tool when you need to filter for suitable dates

Open the calendar