To calculate the date for Passover, identify the new moon that falls in late September or early October and then calculate the 14th day of the seventh month following the new moon. The new moon falls at the beginning of each Jewish month, and Passover occurs in the seventh month.
The traditional Jewish calendar consists of months that relate to the phases of the moon. The new moon occurs at the beginning of the month and the full moon occurs in the middle of the month. Religious observers celebrate Passover on the 14th day of the Jewish month of Nisan.
The new year and the first month in the Jewish year begin with the new moon in September or October. Jews celebrate the new year by observing Rosh Hashana.