#roshhashanah (Head of the Year) is also known as #yomteruah (Day of Shouting or Day of Trumpets), Yom haZikaron (Day of Remembering), and Yom haDin (Day of Judgment). Although the term Rosh Hashanah is not explicitly applied to this day in the Bible, it is considered to be a New Years Day in Jewish tradition for a few reasons:

1-It is thought to be the anniversary of the creation of Man on the 6th day.
2-It is the traditional day of the year on which kings are crowned.
3-It marks the beginning of the Jubilee and Sabbatical years.
4-It is thought to be the day on which God judges mankind for the previous year.

Rosh Hashanah is on the first day of the month of Tishrei. For the purposes of calendars and holy days, God said that the first day of Nisan is the first day of the year, but every culture has multiple annual cycles and new years days.

http://www.americantorah.com/2....016/10/02/happy-new-