Reading a Chinese lunar date

The month begins with a new moon

Traditional Chinese calendar months follow lunar cycles. The first day, written 初一 (chūyī), begins at the new moon. A month contains 29 or 30 days, so its numbered days do not line up with a fixed set of Gregorian dates.

“Eighth lunar month” therefore means the eighth month of that Chinese calendar year. It does not mean August. When a source gives only the lunar month and day, you still need the year before converting it to a Gregorian date.

The day is counted within that month

Days are numbered from one at the start of the lunar month. English references often spell the date out—“the fifth day of the fifth lunar month”—because a numeric form such as 5/5 can be mistaken for May 5.

A leap month repeats a month number

The calendar must keep lunar months aligned with the seasonal year. In some years it inserts a leap month. That month repeats the number of the preceding regular month, so “second month” and “leap second month” are two different dates.

A converter must record whether the month is regular or leap. Leaving that detail out can produce a plausible-looking but incorrect Gregorian date.

Why the Gregorian date changes

Twelve lunar months are shorter than a solar year. Leap months periodically bring the calendar back into relation with the seasons, but the result is that a lunar festival moves across the Gregorian calendar. Mid-Autumn remains on the fifteenth day of the eighth lunar month while its Gregorian date changes from year to year.

The Chinese calendar is therefore more precisely described as lunisolar, not purely lunar. It uses lunar months together with solar terms and seasonal alignment.