When the Chinese new year falls
The date moves because the year is counted by the moon and held in place against the sun.
How many days until the next Chinese New Year
A date that will not stay still
The question usually arrives twice. First: when does the Chinese year begin? Then, once two answers have been found and compared: why are they not the same date?
The confusion is reasonable, because the Gregorian calendar teaches the opposite habit. A birthday, a fiscal quarter, a national holiday — these sit on a fixed date, and the calendar does the adjusting quietly underneath. A reader who expects the Chinese new year to behave the same way looks for one date and finds a scatter: late January in some years, well into February in others, and no obvious pattern in which is which.
There is a pattern, and it is not a drift. The movement is produced by a single rule about how the months are counted, and once that rule is stated the scatter turns into something with edges: a bounded window, two distinct kinds of year, and a boundary that steps backwards and forwards inside those limits instead of wandering off.
Twelve months, and sometimes thirteen
The Chinese calendar is lunisolar. Its months follow the moon, so each one begins with a new moon, and the year as a whole is kept in step with the sun. Twelve lunar months fall short of a solar year, so if nothing were done the new year would slide steadily backwards through the seasons. A thirteenth month is inserted in some years to hold it in place. That is the whole mechanism.
The insertion is visible in the intervals themselves. Across the boundary table's 199 intervals — the gaps from one new year to the next over the Gregorian years 1901 to 2100 — the lengths fall into two groups with nothing between them. A year of twelve lunar months runs 353, 354 or 355 days, and 126 of the intervals are that length. A year carrying the inserted thirteenth month runs 383, 384 or 385 days, and 73 are. The gap between the two groups is about a lunar month wide, because it is the inserted month.
After a short year the next boundary falls earlier in the Gregorian year; after a long one it jumps later. The date sawtooths rather than drifting. Across the Gregorian years 1901 to 2100, which is 200 boundaries, the earliest start is 21 January, in 1966, 2061 and 2099, and the latest is 20 February, in 1920 and 1985. That is a window 31 days wide, and every one of its 31 days is used by some year. 70 of the boundaries fall in January and 130 in February.
Finding the boundary for a given year
Two practical things follow. The first is that the year label cannot be read off a Gregorian date alone near the turn of the year: a day in late January or early February may belong to either side of the boundary, and which side it falls on has to be looked up rather than assumed.
The second is that the animal is a matter of counting, not of lore. It advances by one at each boundary through a cycle of 12, so once the boundary for a year is known, the animal that year carries follows from it directly.
This site holds both halves of that. The pages for the twelve signs list the boundaries themselves, year by year, so a single animal's spans can be read in one place. The converter handles any individual date, across the Gregorian years 1800 to 2100 and the Persian years 1178 to 1479. Between them there is no need for an almanac and no need to guess from memory.
Sources
- Hong Kong Observatory, Gregorian–Lunar Calendar Conversion Table (DATA.GOV.HK)
- Hong Kong Observatory, 1984 Jia-Zi sexagenary-cycle anchor