Jewish calendar

Jewish calendar, showing Adar II between 1927 and 1948 C.E.

The Jewish calendar, also known as the Hebrew calendar, is the calendar traditionally used by the Jewish people. It has been used since Biblical times, and is still used today for Jewish religious observances and as an official calendar of the State of Israel. It determines the dates for Jewish holidays and public reading of Torah portions, and has other ceremonial uses: notably, the yehrzeit, or anniversary of a death, is observed according to the Hebrew date of that person's passing.

When researching Jewish ancestors, knowing how to interpret and convert Jewish dates is essential, as historically, Jews often referred to the Jewish date and/or to the weekly Torah portion when dating letters and other documents. The headstones in Jewish cemeteries almost always note the Hebrew date of the person's death (for yehrzeit observance) and may also include the Hebrew birthdate.

Structure of the Jewish calendar

The months of the Jewish calendar corresponding to the months of the Gregorian calendar

The Jewish calendar is a lunar-solar calendar, meaning it combines lunar months with solar years. The calendar operates on a 19-year cycle, with seven of these years being leap years that contain an additional month (Adar II) to prevent the calendar from drifting too far from the solar year. Each month begins with the sighting of the new moon, or molad, and consists of either 29 or 30 days.

The months of the Jewish calendar are as follows:

1. Nisan (March-April)
2. Iyar (April-May)
3. Sivan (May-June)
4. Tamuz (June-July)
5. Av (July-August)
6. Elul (August-September)
7. Tishrei (September-October)
8. Heshvan (October-November)
9. Kislev (November-December)
10. Tevet (December-January)
11. Shvat (January-February)
12. Adar (February-March)

Though there is reference to months in the Hebrew Bible, they are indicated only by number and not by name. The names used currently are borrowed from the Persian calendar that was used during the Talmudic period, when the Hebrew calendar was standardized.

The regular years, known as "Common Years," have 353, 354, or 355 days while leap years contain 383, 384, or 385 days. This variation is due to the calendar's attempt to reconcile the lunar cycle of approximately 29.5 days with the solar year of approximately 365.25 days.

Historical development of the Jewish calendar

The origins of the Jewish calendar trace back to biblical times. The Torah refers to months by number rather than name, starting with Nisan, which is considered the first month (Exodus 12:2). While the exact system of intercalation used in early times is debated, by the time of the Second Temple period, a more formalized system was emerging.

Hillel II, in the 4th century CE, is traditionally believed to have established the fixed calculated calendar system still in use today. This was done to maintain consistency and unity among Jewish communities at a time when the centralized authority of the Sanhedrin was diminishing. This calculated calendar, also known as the fixed calendar, employs mathematical calculations to determine the beginning of each month and the allocation of leap years.

Medieval and modern times brought adjustments to the calendar, as Jewish communities navigated the complexities of maintaining the lunar-solar harmony. The need for accurate calculations led to the introduction of algorithms and mathematical tools to determine the calendar's intricacies.

Anno Mundi: calculating the Jewish year

The Anno Mundi (AM) system is a calendar era based on the biblical accounts of the creation of the world and subsequent history. The AM system is used in Judaism to count the years since the creation of the world.

The AM system is based on the calculation that the world was created on October 7, 3761 BCE, according to the proleptic Julian calendar. The Jewish calendar year begins on Rosh Hashana, the Jewish New Year.

For example, the Gregorian year of 2023 began during the Jewish year of 5783, which commenced on the Jewish New Year (Rosh Hashana) in September of 2022.

The AM system is not used by any other religious or secular calendar systems. However, it is still used by some Jewish scholars and historians to date events in Jewish history.

The 4 Jewish "new years"

According to Jewish tradition, there are actually 4 distinct "new years" occurring throughout the year that affected different aspects of the ancient Jewish community's religious, political, and agricultural life. The 4 new years are as follows:

• The new year for years and kings (Rosh Hashana, 1 Tishrei): This new year is the most widely known and the most important in the modern Jewish calendar. This is the new year as it is commonly understood in other cultures: the first day of the new year. The reigns of ancient kings of Israel were also calculated by this date.
• The new year for months (1 Nisan): Though the year begins on the first of Tishrei, Nisan is considered "the first month" as mentioned in the Bible, and accordingly, it is the new year for months.
• The new year for trees (15 Shvat or "Tu B'shvat"): Various Biblical laws relating to agriculture require the calculation of a tree's age. For this purpose, the Talmud designated the 15th of Shvat as the "birthday" of all trees.
• The new year for animals (1 Elul): Similarly to the necessity of a "birthday" for trees, the 1st of Elul was designated as a "birthday" of all animals for the purpose of calculating their age for ritual religious needs.

Reading Hebrew dates

A Jewish headstone with a Hebrew date (19 Tamuz 5696) in Lviv

Traditionally, the Hebrew date is written in Hebrew using a system known as gematria, which employs the Hebrew letters rather than Arabic numerals. Each letter of the Hebrew alphabet signifies a number, with the first 10 letters (א, ב, ג, ד, ה, ו, ז, ח, ט, י) standing for the numbers 1-10, the following 9 (כ, ל, מ, נ, ס, ע, פ, צ, ק) indicating 20-100, and the remaining 3 (ר, ש, ת) indicating 200, 300, and 400 respectively. So, for example, the number 7 is indicated by a ז, while 17 would be י"ז, and 27 would be כ"ז, and so forth. The exceptions are the numbers 15 and 16, which are written ט"ו (equivalent to 9+6) and ט"ז (equivalent to 9+7) to avoid spelling out the name of God.

Because this system only has numerals going up to 400, indicating numbers larger than 499 means adding more letters, and as the numbers move into the thousands, this can get quite lengthy. If the Hebrew year is 5783, writing it out fully would require 17 digits! For this reason, the Hebrew year is generally written with a ה at the beginning to indicate the number of thousands (5), and then the year beginning with the hundreds: in the case of 5783, just 783. So the year 5783 is written ה'תשפ"ג, though the ה at the beginning is often left out, leaving simply תשפ"ג.

Hence, the date of 7 Nisan, 5783 may be written ז' בניסן, תשפ"ג or ז' בניסן, ה'תשפ"ג.

The name of the Torah portion being read that week, or of a holiday celebrated that day, or a significant Sabbath (such as the Sabbath before the holiday of Passover, called Shabbat HaGadol, "the Great Sabbath") may also be used alongside or instead of the calendar date in Hebrew or Yiddish documents and letters.

Converting Hebrew dates to Gregorian and vice versa

Because of the complex nature of the Hebrew calendar, it's best to use an online Hebrew-Gregorian date converter to determine the Gregorian equivalent of a Hebrew date, for example HebCal.com.

One important thing to keep in mind is that the Jewish day begins at sundown rather than at midnight, so the time of day an event occurred may affect the conversion to and from Hebrew dates. For example, if a couple was married on March 29, 2023, one might assume that the Hebrew date was 7 Nisan, 5783; however, if the wedding took place at night, the Hebrew date would actually have been the 8th of Nisan. Sometimes, the phrase "אור ל" ("light unto") may be used to indicate that the date is referring specifically to the nighttime portion of the day. So for example, if the ketuba (marriage contract) lists the date of the wedding as "אור ל-ח' ניסן ה'תשפ"ג," that means they got married after sundown on March 29, 2023.

Complicating matters further, there is a disagreement in Jewish tradition about whether a Jewish day begins exactly at sundown (when the sun sinks below the horizon) or at nightfall (upon the emergence of 3 stars). The period between sundown and nightfall is referred to as בין השמשות ("bein hashmashot", literally "between the suns").

Entering Hebrew dates into your family tree

MyHeritage's Family Tree Builder software allows users to enter Hebrew dates into profiles on the family tree. With the online tree or with other family tree building software, it may be necessary to include the Hebrew date in the notes or the bio section.

Explore more about the Jewish calendar

• Understanding Historical Dates and Calendars for Genealogical Research: article by James Tanner on the MyHeritage Knowledge Base
• Understanding Dates: Five Common Mistakes to Avoid on the MyHeritage Blog
• HebCal: Jewish holiday calendar and date calendar

References

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