The "first month" of the Jewish calendar is the month of Nissan, in the spring, when Passover occurs. However, the Jewish New Year is in Tishri, the seventh month, and that is when the year number is increased. This concept of different starting points for a year is not as strange as it might seem at first glance. The American "new year" starts in January, but the new "school year" starts in September, and many businesses have "fiscal years" that start at various times of the year. Similarly, the Jewish calendar has different starting points for different purposes.

The names of the months of the Jewish calendar were adopted during the time of Ezra, after the return from the Babylonian exile. The names are actually Babylonian month names, brought back to Israel by the returning exiles. Note that most of the Bible refers to months by number, not by name.

The Jewish calendar has the following months:
Name Number Length Gregorian Equivalent
Nissan 1 30 days March-April
Iyar 2 29 days April-May
Sivan 3 30 days May-June
Tammuz 4 29 days June-July
Av 5 30 days July-August
Elul 6 29 days August-September
Tishri 7 30 days September-October
Cheshvan 8 29 or 30 days October-November
Kislev 9 30 or 29 days November-December
Tevet 10 29 days December-January
Shevat 11 30 days January-February
Adar 12 29 or 30 days February-March
Adar II 13 29 days March-April

In leap years, Adar has 30 days. In non-leap years, Adar has 29 days.