Why Chinese New Year falls on a different date every year

Chinese New Year is the first day of the first lunar month. Lunar months start on the day of a new moon, and the calendar is arranged so that the winter solstice always falls in the 11th month. That puts the New Year at the second new moon after the winter solstice, and since new moons do not line up with the Gregorian calendar, the date moves every year.

From 1901 to 2100 it falls between Jan 21 and Feb 20: 70 times in January and 130 times in February. The next one is February 6, 2027.

The 11-day pattern

Twelve lunar months are about 11 days shorter than a Gregorian year, so the New Year usually comes 10 to 12 days earlier than the year before. When the lunar year has a leap month, the next New Year jumps 17 to 20 days later instead.

The 19-year repeat

235 lunar months are almost exactly 19 solar years (the Metonic cycle), so the New Year date comes back to nearly the same day after 19 years, often to within a day.

The one exception

From 1902 to 2100 the New Year is the second new moon after the winter solstice every time but once: 2034. The 2033 lunar year has a leap 11th month after the solstice, so the 2034 New Year, February 19, 2034, is the third new moon. Chinese leap months explains why.

Beijing time decides the date

The Chinese calendar is computed for China Standard Time (UTC+8). The New Year date is the same everywhere you celebrate it, even where the new moon happened the evening before by local clocks. Countries that compute their own lunar calendar for their own time zone, such as Vietnam, occasionally get a different date.