What is the first day of the year called in the Gregorian calendar?

The first day of the year in the Gregorian calendar is called New Year’s Day.

New Year’s Day occurs on January 1 in the Gregorian calendar, the civil calendar used by most countries today. It follows New Year’s Eve, which is December 31, and begins the calendar year after the midnight transition.

January 1 was retained as the beginning of the year when Pope Gregory XIII introduced the Gregorian calendar in 1582 to correct drift in the older Julian calendar. Adoption happened at different times in different countries, so January 1 did not become a universal civil New Year date immediately.

New Year’s Day is distinct from religious or cultural new years that fall on other dates, including Lunar New Year, Rosh Hashanah, Nowruz, and the Islamic New Year. Even where another New Year is culturally important, January 1 may still be the official civil-calendar holiday.