There are two Chinese calendars, a solar calendar and a lunar calendar (more precisely, a solilunar calendar, what some call a 'lunisolar' calendar). Both calendars depend on the times of certain astronomical events, principally dark moons and winter solstices. For at least several centuries (according to some scholars, since the 5th C. BCE) the times of these events have been ascertained not by observation but rather by calculation, so these calendars can be classified as rule-based.

The Chinese solar calendar denotes a series of solar years which are divided into "solar terms". The Chinese lunar calendar denotes a series of lunar years which are divided into lunar months. A solar year always begins at the (northern) winter solstice, on or around December 21st in the Common Era Calendar. A lunar month always begins on the day of a dark moon. The beginning of a lunar year (i.e., lunar new year's day) is more difficult to define (but see below); it always begins from about January 20th to about February 20th, i.e., about a month or so after the start of the Chinese solar year.

The Chinese calendar assumes a prime meridian of 120 degrees East. This means that a day (or rather, a nychthemeron, a day and a night) is taken to run from midnight Beijing standard time (BST) to the next midnight BST. This is in contrast to the Common Era Calendar, where a nychthemeron runs from midnight Greenwich Mean Time (GMT) to the next midnight GMT. The time difference between Beijing and London is eight hours, so nychthemerons (or nychthemera) in the Chinese calendar begin eight hours earlier than days in the Common Era Calendar.

Before proceeding further we define some terms:

A dark moon occurs when the Sun and the Moon are astronomically conjunct (or more exactly, when either the Moon's center lies on the line joining the centers of the Earth and the Sun or the plane defined by the Sun, Earth and Moon is perpendicular to the Earth's orbital plane).

The term "new moon" is not used here, since it is ambiguous. It can mean either a dark moon or the phase of the Moon when a crescent is first visible (in which sense a month in the Muslim calendar begins at new moon).

A lunation is a passage of the Moon from one dark moon to the next. A lunation begins at the dark moon (astronomical conjunction of Sun and Moon), and the next dark moon marks the beginning of the next lunation.

An equinox occurs when the angle formed at the Earth's center between its axis of rotation and the line joining the Earth to the Sun is a right angle. At such a point in the Earth's orbit the length of day and night is equal. The northern vernal equinox occurs around March 21st of each year, and the northern autumnal equinox occurs around September 21st.

A solstice occurs when this angle reaches a maximum or a minimum. At such a point the duration of the day and the night is either longest or shortest. The northern winter solstice occurs around December 21st of each year, and the northern summer solstice occurs around June 21st.