Chinese New Year fell on January 22 in 2023, February 10 in 2024, January 29 in 2025, and February 17 in 2026. That’s a swing of nearly four weeks across four consecutive years, and none of it is random. Every date traces back to a specific rule involving the moon, the sun, and a calendar system that predates the Gregorian one by roughly two thousand years.

The Rule Behind the Date

Chinese New Year is not fixed to the solar calendar because it is not calculated from the solar calendar at all. It comes from a lunisolar system, one that tracks both lunar phases and the sun’s position simultaneously. The specific rule is this: the new year begins on the second new moon after the winter solstice, which always falls around December 21 or 22. Because new moons don’t line up neatly with the Gregorian calendar, that rule pushes the holiday somewhere between January 21 and February 20 every single year, never earlier, never later.

Why Twelve Moons Aren’t Enough

A lunar month, the time from one new moon to the next, lasts about 29.5 days. Twelve of them add up to roughly 354 days, which is 11 days short of the solar year. Left uncorrected, a purely lunar calendar drifts backward through the seasons by about a third of a month annually, the same drift behind Ramadan’s shifting dates in the purely lunar Islamic calendar. The Chinese calendar avoids that drift by inserting an extra leap month roughly every two to three years, keeping the new year anchored to late winter instead of slowly sliding into summer or fall.

That 19-year pattern, called the Metonic cycle, means 7 out of every 19 years on the Chinese calendar contain 13 months instead of 12. Which specific month becomes the extra one isn’t arbitrary either. Chinese astronomers track 24 solar terms across the year, and any lunar month that fails to contain one of the 12 principal terms, called a zhongqi, gets designated the leap month and repeats the name of the month before it.

How the Exact Day Gets Picked

Two conditions have to be satisfied together. First, the new moon has to fall after Dahan, or Great Cold, the final solar term of the old year. Second, it has to be the second new moon following the winter solstice, unless a leap month intervenes, in which case the new year shifts to the third new moon instead. Both conditions depend on the exact moment a new moon occurs, which is why the calculation is done relative to a specific time zone. China’s civil calendar runs on UTC+8, so a new moon that lands late in the day in Beijing can technically fall on the previous calendar day somewhere further west, a small but real source of date discrepancies between neighboring lunisolar calendars.

Four Years, Four Very Different Dates

The gap between the earliest and latest possible dates, January 21 versus February 20, is almost exactly one lunar month wide. That’s not a coincidence. It reflects the built-in tolerance of the second-new-moon rule, which can only ever land within a single lunar cycle of its earliest possible occurrence.

One Festival, Several Names and Calendars

Vietnam’s Tết Nguyên Đán and Korea’s Seollal both follow the same core rule, a lunisolar calendar anchored to the winter solstice and a new moon. Korea’s modern calculation method matches China’s closely enough that Seollal almost never lands on a different day. Vietnam is the exception, because Vietnam runs on UTC+7 while China runs on UTC+8, a one-hour gap that occasionally puts a new moon on opposite sides of midnight in the two countries. In 1985, that single hour of difference was enough to push Tết a full month ahead of Chinese New Year, since the new moon landed on different calendar days in each time zone and triggered a different leap month calculation for the rest of that year.

The Zodiac Layer Riding on Top

Each new year also advances a 12-year cycle of zodiac animals, rat, ox, tiger, rabbit, dragon, snake, horse, goat, monkey, rooster, dog, and pig, paired with a rotating set of five elements, wood, fire, earth, metal, and water. Combined, those two cycles don’t repeat the exact same year until 60 years have passed, a sexagenary cycle historically used across East Asia for far more than counting birthdays. It’s the same layered logic behind other moveable holiday dates built from more than one astronomical cycle at once.

Every app and printed calendar that shows Chinese New Year today is still running a rule built for sky-watchers with no telescopes, not one written for software. worldtimedata

A Calendar That Never Actually Left

China officially adopted the Gregorian calendar on January 1, 1912, under the newly formed Republic, demoting the lunisolar system to what became known as the “agricultural calendar,” used mainly by farmers and for setting festival dates. It took until October 1, 1949, when the People’s Republic was founded, for the Gregorian calendar to become the country’s universal civil standard. Even then, the older system never actually lost its grip on the one date that matters most to hundreds of millions of people every winter, and more than a century after being administratively sidelined, it still decides the single biggest travel and family event on the calendar.