The Jewish Calendar

For a podcast discussion of this article click here. For a discussion on the reckoning of months and years in Karaite Jewish Tradition.

The Jewish calendar is based upon the methods and descriptions provided in the Torah for calculating the passage of time. Rabbinical and Karaite traditions surrounding the calendar and its calculation vary. This article is about the different calendar systems Judaism uses, the timing of the holidays, and the history of calendars as they have held influence in Judaism.


Biblical Calendar

The Torah refers to months by number. Shemot (Exodus) 12 describes the first month, during which the Pesach offering and the seven-day Chag Hamatsot (pilgrimage festival of unleavened bread) take place. Other months follow: the Second Month, the Third Month, and so on. Occasionally, months are given names based upon what happens in that month. In later biblical books, the First Month is called the month of “Aviv” or spring. Although the Torah includes mention of months, the text is not specific about what constitutes a month. The text assumes the reader will know because there is a calendar already in use.

We deduce that each month is based upon the lunar cycle by inference. The word for “month” (Chodesh) is from the same root as “new” (Chadash) and there are also references to new moon festivals in the Torah and later books. Bemidbar (Numbers) 28:11 refers to offerings to be made at the new moon festival, for example. The significance of the new moon strongly suggests that it is tied to the new month, but again it is not identified specifically. The lack of particular detail indicates that there was a calendar in use by the Israelites at the time of the Exodus and that the details of the calendar are to be calculated and provided for by the institutions established under the Torah, most likely by the Cohanim (priesthood).


Lunar months vary in length, as the lunar cycle is 29.5 days, lunar months alternate in length between 28 and 30 days. There are 354 days in a twelve month lunar year, leaving the lunar year about 11.25 days short of a solar year. The ancient Chaledeans (Babylonians) calculated a means of reconciling the lunar calendar with the solar calendar. The Chaldean calendar corrects for the 11.25 day shortfall, a thirteenth month is added every few years, seven times in 19 years. These leap years keep the lunar calendar in approximate alignment with the solar seasons. Rabbinical Judaism continues to use the Chaldean calendar while the Karaite calendar corrects for the visibility of the new moon. Rabbinical Jews call this calendar the Hillel II calendar, for they claim it was given under his authority and that of the Rabbis of that time, but it is simply the Chaldean calendar. Rabbinical Judaism also uses the Chaldean names for the months, several of which are named for false deities.

In Karaite tradition, the calendar is corrected for the solar year by determining the ripeness of the barley. The barley crop was destroyed by the plague of fire and ice (volcanic hail) which fell in Egypt. Shemot (Exodus) 9:31-32 refers to the barley being at a state of aviv (ripeness) when it was destroyed. The Torah also refers to the First Month as the month of Aviv. The inference here being that the state of the ripeness of the barley indicates when the month of Aviv may begin. If the barley ripens before the end of the Twelfth Month, the First Month (Aviv) begins at the next new moon. If the barley does not ripen by the new moon, a thirteenth month is added, as the ripening of barley is based upon the solar cycle. This is similar to the Chaledean calendar but corrected for the visibility of the new moon.

Even if the Chaldean calendar used by the Rabbis is not corrected for the visibility of the new moons, it continues to have merit.  Jews all over the world are able to know when to expect the holidays. It is likely the priests informed the disparate communities of the anticipated dates in advance so Jews would know when to travel to Jerusalem for the holidays. Likewise today, Jews can know the holiday dates far in advance. For not being corrected for the precise lunar sightings, honestly the calendars sole flaw, the dates given by the Chaldean calendar are very close to those given by the lunar corrected calendar. Often, the lunar corrected date is just one or two days later. Sadly, the Karaite community struggles to put out a calendar each year to give the holiday dates and to disseminate this calendar to all of its disparate communities; whereas the Rabbinical Chaldean calendar can be used everywhere.

The annual lunar calendar is shorter than the solar calendar, as mentioned before. Even when corrected for the solar year, the holidays observed on the lunar calendar appear to “float” around on the Western solar calendar.  The solar year upon which the modern Western calendar (Gregorian) is based has 365 days and includes a leap day every fourth year to account for the extra quarter of a day. When it comes to Jewish holidays, Yom Kippur might be September 28th this year and September 17th the next. They never occur on the same day in consecutive years. If the lunar calendar went uncorrected, if there was no 13th month added for seven leap years in every 19 year cycle, Yom Kippur would keep moving into the summer and eventually into the spring, as happens with Muslim holidays in their uncorrected lunar calendar. Ramadan, thus, floats around the year and occurs in many different seasons.

Why Correct the Lunar Calendar to the Solar Year?

Many Jewish holidays are set for particular seasons or times of the year. The calendar must be corrected to align it with the solar year to maintain this alignment. The Earth’s orbit around the sun is a quarter of a day longer than 365 days, which is why a leap day is added to every fourth February on the Western calendar. The leap day prevents the solar calendar from floating even an entire day out of alignment. Whereas an extra day can be added to our solar calendar, extra days cannot be easily added to a lunar calendar. These would throw the calendar out of sync with the lunar cycle and defeat the purpose of a lunar calendar. As a result, no less than an entire leap month, one whole lunar orbit, must be added every two or three years (seven in a 19 year cycle) to bring the calendar into alignment with the solar year. In the example of Yom Kippur above, when Yom Kippur comes in the middle of September, the next year will likely be a leap year and Yom Kippur could come in early October, nearly a full month later than the previous year.

In Karaite Jewish tradition the months are based closely upon the new moons. Karaite communities were often disparate, and communication amongst communities took time. Therefore, communities used local new moons to calculate their calendars. The first sliver of the new moon may be visible in Israel on a given Monday, but not until Tuesday in the Crimea or in Vilnius. There are also Karaite communities in far flung places like Kaifeng, China and Daly City, California. The calendars for these communities are, likewise, based upon local visibility. The Karaite Council of Hakhamim in Ramle, Israel calculates the calendar each year well in advance. The Daily City Synagogue often uses the Rabbinical dates for simplicity and due to the intermarriage of Karaite and Rabbinical families within the community.

Nehemia Gordon has popularized another approach which is used by a small number of Karaites and others interested in Karaism. This is the calendar that has become very popular on the Internet. Proponents of this calendar argue that the new moon must be seen in order to discern the new month. While the Torah includes no such requirement, the sighting is helpful to confirm the accuracy of the calendar. There is no reason that this is the best or only way to observe the dates, but it is one interpretation of the Jewish Calendar. The holiday dates are often the same as those of the Traditional Karaite Calendar if at times a day off, or a couple of days off of the Rabbinical Calendar. Click here to view the lunar observed (aviv observed) calendar.

The Hillel II Calendar

The Rabbinical (Talmudic) calendar is the Hillel II calendar. It is named for one of the last “princes” who purportedly presided over the Sanhedrin. In the late 4th Century, according to Talmudic sources, it became too dangerous for the Sanhedrin to meet and hear witnesses concerning the calendar. At issue is the 19-year cycle by which Rabbinical authorities intercalculate the leap years, based upon the Chaldean calendar. Rather than base the calendar purely on a visual sighting of the agricultural signs, this system mathematically distributes the months such that the leap year will most likely align with the ripening of the barely. Since the Torah provides no specific instruction that the ripe barley must be seen, it is implied that a calculation for it could suffice. According to Talmudic tradition, Hillel II left instructions for this 19-year leap year cycle in his time such that the Sanhedrin would not have to meet to hear witnesses. This 19-year system intercalculates seven leap months such that the 19 lunar years equal 19 complete solar years. Many scholars ascribe this development as a feature of the Chaldean (Babylonian) calendar.

Rendering of the Sanhedrin

Based upon this 19-year cycle, and under the influence of the Chaldean calendar, the modern Rabbinical calendar developed over the years. Though it is called the Hillel II calendar, Hillel II himself played only a minor role in its development. Additional details were included by several Gaonim (great teachers) in the eleventh and twelfth centuries.

In terms of its calculations, with the exceptions described below, the Hillel II calendar is an excellent calendar. Although my family and I would prefer to use the calendar dates calculated by the Karaite community, we often simply use the Rabbinical calendar dates. This calendar allows all Jews everywhere in the world to observe the holidays on uniform dates while observing all of the Torah’s explicit requirements and even meeting many of the inferences. The calculated months approximate the lunar cycle fairly closely if not precisely, for example. It avoids confusion and modernizes the complex methods by which the calendar is calculated. This is similar to the calendar the priests almost certainly published in the times before the Second Temple’s destruction. If this calendar could be properly corrected for the anticipated visibility of the new moon, it would be the ultimate Jewish calendar.

Calendar Craziness

Over the past few years I have become aware of several crazy calendar concepts. One holds that the Vernal Equinox should be used to determine the start of the new year or the need for a thirteenth month. While the Barley certainly has a tendency to ripen close to the equinox and it is an excellent means of correcting for the solar year, as this is certainly a solar inspired event, there is no basis in Torah for utilizing such a sign to calculate the calendar.

Yet another crazy theory holds that it is the full moon that should determine the start of the month rather than the first visible sign of the moon. The inference drawn from the Torah is clear, a new moon is a new moon, it is either the night when the moon is entirely eclipsed by the Earth or it is when the first sliver of the moon is visible, as is the Karaite tradition. It cannot be the full moon. Several holidays, the Chag Hamatsot and the Chag HaSukkot are arranged so they will arrive in the middle of the month. Both involve nighttime observances and both will always arrive during the full moon, under the calendar systems in use by Jewish movements today.

The lunar Shabbat is perhaps the craziest theory I have come upon and I must apologize for even offering it a mention here. Under this theory Shabbat is to be fixed as the seventh, fourteenth, twenty-first, and twenty-eighth days of the month. Under this concept no one could rightly know when Shabbat would arrive in any given month. This idea clearly violates the Torah’s explicit commandment (See Shemot [Exodus] 20:7-10 for example) that all Israelites (Jews) rest EVERY seventh day. That does not mean rest after eight or nine days because there were extra days in a given month; the commandment requires rest every seventh day.

Karaite vs Rabbinical Calendars

The greatest difference between the calendars is the new year. According to the Torah (see Shemot 12 cited above), the month during which the Chag Hamatsot takes place (called Nisan on the Rabbinical calendar) is the first month. Rabbinical tradition holds a new year (among others) in the seventh month and converts the one-day holiday Yom Teruah (Day of Shouting) into a two-day new year called Rosh Hashana (first of the year). Where the authority comes from to convert a Torah commanded holiday into a different holiday with a name and purpose entirely at variance with the Torah is unclear, probably because there can be no such authority under Torah. The seventh biblical month does conveniently align with the Byzantine new year, however. Rabbis eager to align Judaism with the lifestyle of the later-Roman (Byzantine) Empire tried to override the correct, written Torah. As a result of this difference, the counting of the months differs between the two traditions.

Rabbinical tradition holds that there are four new years, although there are no scriptural sources whatsoever for the additional three. The first day of the Sixth month (Elul) is considered a new year for tithes, there is the Byzantine new year of Rosh Hashana, and Tu B’Shvat: a new year for trees. The new year for trees also finds its origin in Babylonian paganism and one might note that the worship of trees and presence of holy trees in Temple grounds or near altars is forbidden in the Torah. As much as it might surprise everyone, in Karaite Judaism there is one new year: the first day of the First Biblical month (Aviv). Fourteen days before the Chag Hamatsot (Pesach – Passover) begins at sunset on the 14th day as the 15th day begins. The Rabbis claim this month is a new year only for kings and festivals.

Chaldean Star Calendar Stele

Another area of difference is in the names of the months. The Torah gives the names of each month by number, the First Month, Second Month, Eighth Month, etc. The Torah also refers to the First month as Aviv (spring). The later scriptures, the Neviim (Prophets) and Kethuvim (Writings), also mention a few names for months: the First Month is called Nisan in Esther; the Second Month is called Ziv twice in the First Book of Melekhim (Kings); the same book refers to the Seventh Month as Ethanim

and the Eighth Month as Bul. The origin of these names is not made clear in the written scriptures and it is likely that these were the common names for these months in the times each book was written.

For the most part, the names for months used in the modern Rabbinical calendar are those of the Chaldean calendar and are of Akkadian origin. Many of these names are for Mesopotamian deities like Tammuz. It is shameful that in many traditions Jews continue to practice mourning in the month of Tammuz (the Fourth Month). This is similar to the Gregorian calendar used today in the West in which January is named for the Roman deity Janus, July for the deified Julius Caesar and so on, and the years counted from the purported birth of a deified culture hero. In Karaite tradition the months are officially known by their numbers, although as Jews we often use the Rabbinical names as a common reference.

Roman coin issued in the year 248 CE commemorating the 1001st year since the foundation of Rome (AUC)

The Rabbinical counting of the years is also an interesting topic. In the autumn of the year 2022 the year 5783 begins according to the Rabbis. This counting purports to be from the creation of the world. This system for counting the years is, however, based upon the Roman calendar. Roman historians like Livy occasionally, but unofficially, used a dating system that has come to be known as Ab Urbe Condita (AUC), from the foundation [of Rome]. This system of counting has 753 years more than the Gregorian calendar set by a Pope who sought to set the first year as the birth of the Christian culture hero. When we add those years to the current year (2022 + 753) we find that this year began the Roman year 2775.

Curiously, if you add 3007 to the current year AUC you will arrive at 5782, which is the current year on the Rabbinical calendar. The Rabbis seem to have added 3007 to the Roman calendar in order to arrive at their counting of years. This is too great a coincidence to the unintentional. Karaite Judaism does not use this counting of the years. The ancient Israelites counted dates from the Exodus from Egypt and the Prophets strongly imply that later Jews should count the years from the return from the exile in 538 BCE. By that counting the current year (2022 +538) would be 2560.

Holiday Differences

The most obvious holiday difference between Karaites and Rabbinical Jews is that Karaites continue to observe Yom Teruah as the first day of the Seventh Month, as is written in the Torah. It is the Torah that Jews should observe, not the Byzantine New Year. Rabbinical tradition also includes several other holidays, including three additional new years observances and the Lag B’Omer in which Rabbinical Jews celebrate around bonfires. Karaite Jews do not observe these additional holidays. The Rabbis also move Purim to the leap month (Adar II) in every leap year, whereas in Karaite Jews always observe this day in the Twelfth Month as the Book of Esther asks all Jews to do. These traditional holidays are not included in the Torah and do not rise to the same station as those found in the Torah. There is no prohibition against having additional observances, adding holidays and claiming that they are commanded in the Torah is prohibited.

One more and very significant difference between the two calendar systems centres on the the counting of the Omer and the date of the Chag HaShavuot (pilgrimage festival of weeks). The differing interpretations rest upon the interpretation of Vayikra (Leviticus) 23:15:

You shall count from the morning after the Shabbat השּׁבּת [day of rest], from the day that you brought the Omer offering [sheaf of the waving]; seven Shabbats שׁבּתוֹת [Shabbats] you shall complete.

In Sadducee, Karaite, and Samaritan practice, the passage is interpreted such that the day of the Omer, which commences the counting, is the day after the first Shabbat during the seven days of the Chag Hamatsot. Seven weeks proceed from there, each punctuated by a Shabbat. Note that in the verse above it clearly states that the first day, the day of the Omer offering, is the day after Shabbat and that seven Shabbatot (Shabbats) are to be counted thereafter; not seven weeks as the Rabbinical tradition holds. Given that many translations serve the interpretations given by the Rabbis, these translations are often given as “seven weeks,” misleadingly. Click here to see the Hebrew and English side-by-side. The Temple Scroll among the Dead Sea Scrolls also confirms this method of counting the Omer which suggests that in ancient times, Jews counted the Omer as Karaites do today.

In the Karaite tradition, the Chag HaShavuot is always on the Yom Rishon (Sunday) which follows the seventh Shabbat after the day of the Omer. Where the day of the Omer is always the Yom Rishon (Sunday) after the first Shabbat that occurs during the seven days of the Chag Hamatsot (Passover). Talmudic tradition, however, holds that the word Shabbat used in verse fifteen refers to the first day of the Chag. Verse seven of the same chapter says no work is to be done on the first day of the Chag, but this is clearly not Shabbat, nor is the word Shabbat used. For this reason, the Rabbinical counting of the Omer begins from the second day of the Chag Hamatsot, irrespective of what day of the week it is, and counts 49 days from there, with Shavuot arriving whatever day of the week happens to be the 50th. The use of the plural of Shabbat (Shabbatot) in the second sentence of verse 15 (quoted above) makes the meaning inescapable, as it is the Shabbats that are to be counted, not just the weeks. Rabbinical tradition prohibits Shavuot from coinciding with Shabbat despite the incongruous method of counting. The Rabbinical tradition is thus clearly divorced from what is written. There is no textualist argument which can defend the Rabbinical interpretation.

History of Near-Eastern Calendars

Karaite gathering at the Synagogue in Daly City

The Torah tells us that Avraham and his family were originally from Ur, an ancient Sumerian city-state. The Sumerians, contributed greatly to the calculation of calendars; in fact our modern means of telling time is largely based upon the Sumerian model.

Ancient civilizations often kept several calendars. Egypt utilized both lunar and solar calendars of varying accuracy, and a lunisolar calendar with intercalculated leap years similar to the Chaldean calendar used by modern Rabbinical Jews. These calendars existed long before the Habiru/Hebrews resided there. As a result, the Israelites would already have had a system for calculating the calendar that they would have used upon their departure from Egypt. Much like the details of slaughtering, which were commonly understood at the time and need not be given in detail, the precise details of the calendar are vague because there was already a calendar in use. For that reason, the Torah makes only indirect references to the months.

7 thoughts on “The Jewish Calendar

  1. “Since the Torah provides no specific instruction that the ripe barley must be seen, it is implied that a calculation could suffice.”
    Don’t you need barley for the Omer offering? You are commanded to make sure the Passover is always celebrated in the month of the aviv. How does one know if the barley is in aviv if it is not seen? Some factors that cause barley to ripen include temperature and wetness. I haven’t seen weathermen consistently get it right yet. It’s God’s world and He makes things happen as He pleases. Our mission, if we accept, is that we are to follow along.


  2. I am not aware of any year in which the Barley was not ripe for harvest well before the date set for the first day of the Chag Hamatsot (Pesach) on the Hillel II calendar. I would very much doubt that this would ever be a problem. The way the calendar is calculated, the barley will always ripen and the harvest will be done before the Chag begins.


  3. I’m confused on the use of the calendar. Do Karaites use the calendar or do they rely on the new moon sighting? It seems that some are using the new moon and some the calendar. I have been following Rabbinic Judaism and going by the calendar but am very interested in Karaite Judaism but am perplexed by this because everyone is always doing something different.


  4. Traditional Karaite Jews use the precalculated Karaite calendar for the most part. A small few use the lunar sighting. The Karaite community in the United States has used the Rabbinical (Hillel II) calendar for many years out of convenience. Unfortunately, there is no definite answer that we all use one or the other method.


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