Which calendar uses Rosh Hashanah as its New Year, usually in September or October?

The Hebrew calendar uses Rosh Hashanah as its New Year, usually in September or October on the Gregorian calendar. Rosh Hashanah begins on the first day of the Hebrew month of Tishrei and starts the Jewish civil year.

The Hebrew calendar is lunisolar: its months follow lunar cycles, while its year is coordinated with the solar seasons. Because of that structure, Rosh Hashanah moves from year to year when converted to the Gregorian calendar, although it remains within a relatively narrow seasonal range. Hebrew dates begin at sunset, so the holiday starts before the first daytime date shown on many civil calendars.

Rosh Hashanah is part of the Jewish High Holy Days and is associated with prayer, reflection, and the sounding of the shofar, traditionally a ram's horn. It is distinct from the first day of Nisan, which has a different religious significance in the Hebrew calendar. The term “Jewish New Year” can therefore simplify a calendar with several important year beginnings.