A New Year on the seventh month!

About the Jewish New Year

Often people, especially those who are not familiar with the Jewish customs, get confused over the occurrence of the Jewish New Year in the seventh month of the Tishri. Though the Bible speaks of Rosh Hashanah falling on the first day of the seventh month, the question is how people can celebrate a New Year on the seventh month of their own calendar .
Instead it could have celebrated on the Nissan, the first month of the Tishri. And Nissan occurs in March and April.

Here goes an explanation:
Instead of the usual unique one, the Judaism has several "new years," each one dedicated to a specific cause.

The concept, though, may appear strange at first, has got the logic of its own. For instance, the American "new year" starts in January, but the new "school year" starts in September. Again, many businesses have "fiscal years" that start at various times of the year. So, even here we have different new years, each book marked for a different purpose.

Similarly in Judaism, Nissan 1 is the new year for the purpose of counting the reign of kings and months on the calendar.
Elul 1 (in August) is the new year for the tithing of animals.
Shevat 15(in February) is the new year for trees. It helps determining the time when first fruits can be eaten.
Accordingly, Tishri 1, when the Rosh Hashanah is celebrated is the new year for years. This is when Jews start counting the the year number. Sabbatical and Jubilee years begin at this time.

According to historians like Josephus Flavius, Tishrei indeed served as the beginning of the year, based on the tradition that the world was created in that month. But the Torah determined that "This month [i.e. Nisan] is for you the beginning of the months, it shall be the first month of the year to you." All counting is to be in accordance with the Exodus from Egypt. Because by counting this way, Israel is distinguished from the other nations; counting from Nisan marks the date on which God's majesty was revealed to Am Yisrael. And specifically on "yom teru'ah", the day on which Israel's special character is manifest, we understand the idea of counting the year starting from the month of Nisan making Tishrei seventh in that cycle.