Nisan

Nisan (or Nissan; Hebrew: נִיסָן, romanized: Nīsān from Akkadian: 𒁈, romanized: Nissāni) in the Babylonian and Hebrew calendars is the month of the barley ripening and first month of spring. The name of the month is an Akkadian language borrowing, although it ultimately originates in Sumerian nisag "first fruits". In the Hebrew calendar it is the first month of the ecclesiastical year, called the "first of the months of the year" (Exodus 12:1-2), "first month" (Ex 12:14), and the month of Aviv (Ex 13:4) בְּחֹ֖דֶשׁ הָאָבִֽיב ḥōḏeš hāʾāḇîḇ). It is called Nissān in the Book of Esther. It is a month of 30 days. In the year 2025, 1 Nisan will occur on 30 March. Counting from 1 Tishrei, the civil new year, it would be the seventh month (eighth, in leap year), but in contemporary Jewish culture, both months are viewed as the first and seventh simultaneously, and are referred to as one or the other depending on the specific religious aspects being discussed.

The biblical Hebrew months were given enumerations instead of names. The new moon of Aviv, which in Hebrew means "barley ripening" and by extension "spring season"(Exodus 9:31) is one of the few called both by name and by its number, the first. Nisan and other Akkadian-origin names for the equivalent lunar months in the Babylonian calendar came to be applied to the Hebrew calendar during the Babylonian captivity, in which the month of Aviv's name was Araḫ Nissānu, the "month of beginning".

The list below gives a time which can be used to determine the day the Jewish ecclesiastical (spring) year starts over a period of nineteen years. These are not Nisan molad times, although the offset necessarily remains constant. (The fractions shown are fractions of a minute.)

Every nineteen years this time is 2 days, 16 hours, 33 1/18 minutes later in the week. That is either the same or the previous day in the civil calendar, depending on whether the difference in the day of the week is three or two days. If 29 February is included fewer than five times in the nineteen – year period the date will be later by the number of days which corresponds to the difference between the actual number of insertions and five. If the year is due to start on Sunday, it actually begins on the following Tuesday if the following year is due to start on Friday morning. If due to start on Monday, Wednesday or Friday it actually begins on the following day. If due to start on Saturday, it actually begins on the following day if the previous year was due to begin on Monday morning.

The table below lists, for a Jewish year commencing on 23 March, the civil date of the first day of each month. If the year does not begin on 23 March, each month's first day will differ from the date shown by the number of days that the start of the year differs from 23 March. The correct column is the one which shows the correct starting date for the following year in the last row. If 29 February falls within a Jewish month the first day of later months will be a day earlier than shown.

For long period calculations, dates should be reduced to the Julian calendar and converted back to the civil calendar at the end of the calculation. The civil calendar used here (Exigian) is correct to one day in 44,000 years and omits the leap day in centennial years which do not give remainder 200 or 700 when divided by 900. It is identical to the Gregorian calendar between 15 October 1582 CE and 28 February 2400 CE (both dates inclusive).

To find how many days the civil calendar is ahead of the Julian in any year from 301 BCE (the calendar is proleptic [assumed] up to 1582 CE) add 300 to the year, multiply the hundreds by 7, divide by 9 and subtract 4. Ignore any fraction of a day. When the difference between the calendars changes the calculated value applies on and from 1 March (civil date) for conversions to Julian. For earlier dates reduce the calculated value by one. For conversions to the civil date the calculated value applies on and from 29 February (Julian date). Again, for earlier dates reduce the calculated value by one. The difference is applied to the calendar one is converting into. A negative value indicates that the Julian date is ahead of the civil date. In this case it is important to remember that when calculating the civil equivalent of 29 February (Julian), 29 February is discounted. Thus if the calculated value is −4 the civil equivalent of this date is 24 February. Before 1 CE use astronomical years rather than years BCE. The astronomical year is (year BCE) – 1.

Up to the 4th century CE, these tables give the day of the Jewish month to within a day or so and the number of the month to within a month or so. From the 4th century, the number of the month is given exactly and from the 9th century the day of the month is given exactly as well.