Which calendar is used to determine Chinese New Year, which can fall between January 21 and February 20?

The Chinese lunisolar calendar is used to determine Chinese New Year, which can fall between January 21 and February 20 in the Gregorian calendar.

A lunisolar calendar follows lunar months while keeping the year aligned with the solar seasons. Chinese New Year begins on the first day of the first month, and the date changes annually because lunar months do not have the same length or position as Gregorian months.

An intercalary month is added when necessary to keep the lunar calendar synchronized with the solar year. This is why Chinese New Year does not have a fixed Gregorian date, unlike January 1 New Year's Day.

The festival is also called the Lunar New Year in broader international contexts, but not every culture using a lunisolar or lunar calendar celebrates on the same date. “Chinese New Year” specifically refers to the Chinese festival and its associated traditions.