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Ancient Hebrew Calendar


The following reconstruction describes an old Hebrew luni-solar calendar which synchronised the heavenly bodies regularly per seven years, and again in the forty-ninth year. Following that, another forty-nine year cycle would repeat using the same formula. The pattern of leap-years never needed to change, although it does seem there were changes to the Jewish calendar from about the Persian - Greek period, not for the better it might be added, but probably to comply with the governing empires of that time.

The first thing to be noticed is how units of time were distinguished by the 'shabuwa', a word which simply means 'heptad' or 'week'. By contrast, the Egyptian 30-day month was divided into three 'decans' of ten days each, but the Hebrew calendar was strictly sabbatical. The following is a breakdown of time measurement in it:

  • a 'week' of days (7 days)

  • a 'moon' (one month)

  • a 'time' (one year)

  • a 'time, times and half a time' (3½ yrs)

  • a 'week' of years (7 years)

  • a 'jubilee sabbath' (49 years)

  • a '70-week jubilee' (490 years)

The 'week of years' was akin to our 'decade', and 'jubilee' might be likened to our 'century', albeit shorter. The longer '70-week jubilee' is alluded to in both Testaments and is also mentioned in fragments of manuscripts found among the Dead Sea Scrolls. (Scroll 11Q13)

A 'moon' (lunar month) is typically 29 or 30 days, so when the year was completed it only reached 354 days, about eleven days short of the Sun's 365¼ day rotation. As a result, the year slipped back each season, and an extra (thirteenth) month had to be inserted every so often. It was added at the end of Adar, according to a sabbatical formula if my proposition is correct - not according to primitive observation of seasons as it is usually assumed to have been done.

Ancient Hebrew Calendar

"Seven times shall pass over you, until you have learned that the Most High has sovereignty over the kingdom of mortals and gives it to whom he will."

(Daniel 4:16, 32)

Concerning the Modern Jewish Calendar

A common area of confusion concerning the biblical calendar arises from an assumption that the modern Hebrew calendar is the same as the ancient one. It isn't. The misunderstanding is not helped by rabbinic experts either, who make the same assumptions as everyone else. It's a good calendar, it's luni-solar, and it works. Why look for another? Also, a false credibility bolsters the assumption since the modern Hebrew calendar is not really modern. It is similar to, and can be traced back to the Greek, Persian, and Babylonian empires. Now, that is old.

But it is not as old as the one of which we speak. Moses set up a calendar eight hundred years before the Babylonian empire existed. Earliest calendar references go back to the Bible's book of Genesis, but as far as an exclusive Hebrew system is concerned, the first mention is found with instructions given to Moses at the time of the Exodus.

"This month shall be for you the beginning of months. It shall be the first month of the year for you." (Exodus 12:2)

It was the month of Abib (later renamed Nisan) and what is being said here is clear; the first of Abib was to become New Year's Day.

It begs the question: If Moses was given a new start to the year, when was New Year under the calendar from which they had come? The Egyptians called it the "opening of the year" and it started with the star, 'Sirius', which appeared in the sky in July when the first season was ushered in by the flooding of the river Nile. They associated the life-giving inundation of their crops with Sirius, bringer of new life.


In mentioning this I do not mean to discuss the Egyptian Sothic cycle. I only wish to make the point that the Hebrew calendar was not copied from Egypt. The Bible's calendar was unique in its operation and different from neighbouring countries.

Bible Calendar References

The next reference to an exclusively Hebrew calendar is not as obvious because it's other function related to religious festivals and the release of debts. I am referring to the 'Jubilee.'

"Count off seven sabbaths of years - seven times seven years - so that the seven sabbaths of years amount to a period of forty-nine years. Then have the trumpet sounded everywhere on the tenth day of the seventh month; on the Day of Atonement sound the trumpet throughout your land. Consecrate the fiftieth year and proclaim liberty throughout the land to all its inhabitants. It shall be a jubilee for you ... The fiftieth year shall be a jubilee for you." (Leviticus 25:8-11)

However, Jubilee is more than what meets the eye. Apart from radical agriculture and 'debt release' provisions, it contained precisely 600 lunar cycles from the 1st of Abib to the 1st of Tishri in the forty-ninth year! Apparently Jubilee was part of a luni-solar system designed for the keeping of time.

Then there is the Sabbath system itself. There are various descriptions of the Sabbatical years but without any direct mention of calendrical formulas. Perhaps that is why they haven't been noticed. Nevertheless, when looking beneath the surface of the biblical text, the Sabbath 'weeks' contain formulae relating to the placement of intercalary months. We shall look at these soon.

In later references we notice special calendar terms and numbers which occur in the prophetic writings. An example of how a year was called a 'time' is found in King Nebuchadnezzar's bout of insanity. He boasted,

"Is this not magnificent Babylon, which I have built as a royal capital by my mighty power and for my glorious majesty?"

When he was humbled, it lasted for seven 'times' - in other words, for seven years.

"O King Nebuchadnezzar, to you it is declared: The kingdom has departed from you! You shall be driven away from human society, and your dwelling shall be with the animals of the field. You shall be made to eat grass like oxen, and seven times shall pass over you, until you have learned that the Most High has sovereignty over the kingdom of mortals and gives it to whom he will. Immediately the sentence was fulfilled against Nebuchadnezzar. He was driven away from human society, ate grass like oxen, and his body was bathed with the dew of heaven, until his hair grew as long as eagles feathers and his nails became like birds claws." (Daniel 4:16-32)


Similarly, there are mentions of a 'time, times and half a time.' It is 3½ years, and is one half of a Sabbatical cycle. Then, there are the curious numbers of 1260, 1290 and 1335 days which appear in the books of Daniel and Revelation. They have baffled students with commentaries calling them 'unknown calculations' and popular end-time writers dreaming up fanciful ideas as to what they might mean. Please deduct 30 days off 1290. Please deduct 30 + 30 + 15 (2½ mths) off 1335. In both cases it equals 1260 days.

If we select the Day of Atonement, the 10th Tishri, (Ethanim) and add 1260 or 1290 days, it always resets itself to the Hebrew New Year Day, the 1st of Abib, three and a half years later. Our observation suggests that these unusual figures might be intercalations to an underlying calendar.

To demonstrate this, let us take the 10th day of Tishri from a well known historical date in the Babylonian captivity period. Such a year was Judah's first year in captivity, 3175 AM. It equates to our western date, 27th September, 587 BC, and has an astronomical value of 1,507,291. Three and a half years afterwards, 3178 AM, the 1st of Nisan (Abib) equals our western date, 10th March, 583 BC, with an astronomical value of 1,508,551. By deducting the astronomical values we do indeed find a difference of 1260 days! The reason why this figure (and 1290) keeps repeating as described, is because it is mathematically linked to the phases of the moon. The math is as follows:

  • D.of A. to end of Tishri = 20 days

  • end Tishri to end of year = 5 months

  • 3 years x 12 = 36 months

  • 1 intercalary month = 1 month

  • TOTAL MONTHS = 42 mths + 20 days

  • 42 x 29.53 = 1240.26 days

  • TOTAL DAYS = 1260 days

Extra-Biblical References

If a criticism were to be made of my thesis, it might be that detailed case examples do not exist in early writings which explicitly describe the workings of the original Hebrew calendar. Yes, my reconstruction is based on a relatively small number of biblical texts, but that does not mean to say that extra-biblical evidence does not exist as well.

The Babylonian Talmud explains how the legal system during the period of the Judges of Israel kept track of events in terms of Sabbatical and Jubilee cycles. The court would make a formal record of contracts, crimes etc. by writing down the 'Septennnate' (week of years) when the event took place, then by determining the Jubilee cycle in which the Septennnate belonged. For example, "The accused committed the crime on the 1st day, of the 2nd month, of the 3rd year, of the 4th Septennate, of the 5th Jubilee." This information should dispel any doubt as to whether Sabbath years and/or Jubilees were ever practiced or not, at least for the Judges era. It also expresses calendrical terminology.

Such calendar language as described above, is also used in the ancient 'Book of Jubilees', copies of which were found among the Dead Sea scrolls. For example, it relates Jacob's move to Egypt as follows:

"And Israel went into the country of Egypt, into the land of Goshen, on the new moon of the 4th month, in the 2nd year of the 3rd week (of years), of the 45th Jubilee." (Jubilees 45:1)

For whatever else we might think about parabiblical literature, one thing is sure; Jewish readers as early as the second century BC were aware of a former Sabbatic method of dating.

We must challenge the common assumption that the modern Metonic calendar is the same as the biblical one: It isn't! When studying the inter-testament era, it becomes apparent that Babylonian, Persian and Greek elements had been added to it. The all-important month of Abib (Deuteronomy 16:1) reappears after the captivity as 'Nisan,' a Babylonian name. (Nisanu) Sometime after that, Jubilee observances ceased, then New Year was shifted from Abib to Tishri. We don't know exactly when these changes took place. I suspect Jubilee stopped soon after Nehemiah. Hecataeus of Abdera, a Greek historian who lived during the conquests of Alexander, is credited with saying,

"Under the rule of nations during latter times, namely, Persians and Macedonians ... the Jews greatly modified the traditions of their fathers." (Diodorus Siculus 40:31)

Alfred Edersheim adds, "after their return from exile, the Jews dated their years according to the Seleucid era." (The Temple-Its Ministry and Services, ch.10) It is known that the Seleucid New Year was Dios which was the Greek equivalent to Tishri, so it would be fair to surmise that the New Year change came about then.

Also, the Dead Sea Scrolls reveal a serious debate concerning changes to the inter-testament period calendar.

"All the children of Israel will forget and will not find the path of the years, and will forget the new moons, and seasons, and Sabbaths, and they will wrongly determine all the order of the years. For this reason the years will come upon them when they disturb the order ... they will go wrong as to the months and Sabbaths and feasts and Jubilees." (Jubilees 6:33-37)

Thus the Essenes of Qumran rejected the post-Babylonian calendar and the temple authority's festival dates, because they believed the true calendar had been abandoned by the priests and replaced with an alternative system. Their scrolls show instead a 364-day solar year that was divisible by seven. This, they believed to be the original system founded by Enoch, and those who departed from it were "apostate."


Attempts to apply leap-year formulae to the Enochian year have not been satisfactory, but the fact that the Essenes attempted to recover a 'lost' Sabbatical calendar speaks loudly that there was one to be found! The following reconstruction does indeed find such a pre-Metonic calendar, and I would now like to put forward for consideration the precise intercalation formula and astronomical details of the original Hebrew calendar.

Division of the Week

Every luni-solar system, be it Hebrew, Greek or Babylonian, realises that the lunar year needs adjustment about every third year. Therefore it is not by coincidence that the Hebrew heptad of years was divided in half and called, a 'time, times and half a time.' This term is mentioned in the Bible often enough, but usually in a 'prophetic' setting. That aspect is beyond the scope of this article, so we shall limit our discussion of the division of the week to its function in the calendar.

The division occurred; it seems, on Israel's all-important festival, the Day of Atonement. The D.of A. was the 10th of the seventh month, but it should not be supposed an arbitrary date of religious significance only. When we count 3½ years from the beginning of a Sabbatical cycle, it comes to a total of 1278 days to the start of the D.of A. in the middle year. Now, this is interesting, because the number of days in 3½ solar years is the same (3.5 x 365.2 = 1278 days) so the 10th of Tishri must have been a marker showing where the lunar calendar intersects with the solar.

Each heptad of years was divided in two equals 86lunar months equals3.5 x 365.2 2539 days 1260 days 1278 days sabbathyear division of the week onday of atonement in middleof each sabbath cycle time, times + ½ time time, times + ½ time 1st Abib 1st Abib

That is not all. When we count from the end of the Day of Atonement 1260 days, it resets itself, as mentioned before, to the start of the next Sabbatical cycle. So, the special festival in the middle year is actually a 'fulcrum' between two significant counts. Each 'time, times and half a time' had an additional month added to the 'base' 42 months, making 43 lunar months on both sides - a total of 86 lunar months altogether. Please examine the diagram taking note that the Day of Atonement stands independently between the two counts.

Old Testament scripture alludes to the division of the week by Daniel's term, 'midst of the week' although, in this case, it referred loosely to the sacred festival period of the middle year. It also mentions an extra leap month, expanding the 1260 days to 1290 days. By understanding how the number of days count to New Year’s Day, we are provided with part of the answer to what the prophet meant when he said: "From the time that the regular burnt offering is taken away and the abomination that makes desolate is set up, there shall be 1,290 days." (Daniel 12:11) 1290 days to what? The sentence doesn't seem to lead anywhere, and yet the answer is what the reader is looking for! However, Daniel would have expected his original readers to have known that he meant from the Day of Atonement to New Year's Day.

Indeed, when we follow the moon over extended periods, we find the ancient Sabbatical cycle alternating between 86 and 87 months until seven 'weeks of years' completed the Jubilee of forty-nine years. In the case of the alternate 87 months, the equation would show a 'time, times and half a time' of 1278 days on one side, and 1290 days on the other. In other words, a total of three months were added in those cases.

I have checked this model over hundreds of years, and come to the conclusion that by combining the formula with actual sightings of New Moon, the calendar would have been virtually mistake-proof. For a recent example, let us take the 1st of Nisan, 2000 AD and add 1278 days. It comes to the 10th of Tishri 2003 AD. If we count this hypothetical 'day of Atonement' then add another 1260 days, it returns to the 1st of Nisan, 2007 AD. The system is no longer in use of course, but it works just as well today as it did in biblical times! For examples of actual biblical dates, please see my academic paper here:

Placement of Intercalary Months

When seven weeks as described are spread over one Jubilee, a pattern of eighteen intercalary months appears that can be repeated indefinitely in each subsequent Jubilee cycle. Please examine the next diagram showing fifty years divided into blocks of seven. The seventh year (Sabbath) is indicated by a red square and the position of leap-months indicated by green dots. The fiftieth year is shown in purple; and notice how it is superimposed over the forty-ninth year and first year of the following cycle.

There were a total of 18 leap-months every Jubilee cycle 48 ½ solar years= 50 lunar years= 600 months t, t + ½ t1278 days t, t + ½ t1260 days 7 × 12 = 84 mthsleap yrs = 3 mths= 87 mths 13th month neveron a Sabbath year 87 mths 87 mths 87 mths 86 mths 86 mths 86 mths 1st Abib 1st Tishri

As can be seen, the eighteen intercalary months added over forty-nine years created the same overall effect as our modern Metonic system does, but it had a different way of going about it. The Metonic cycle moves gradually through each year, adding months over nineteen years, whereas the Hebrew method was 'Sabbatical' and avoided adding to Sabbath years. It is mentioned in the Rabbinic writings, (Tos. Sanhedrin 2:9) because a 13th month would have increased the seventh year, extending the Sabbath planting restrictions and creating an unnecessary burden on the people.

When compared with modern calendars, a few intercalary months are offset by one year but never did it wander off the seasons. The calendar given to Moses all those years ago worked. Moreover, it worked as well as, if not better, than any system we have today!

There are implications here for liberal scholars and their theories of a primitive Israelitish nation evolving out of Canaan, whose knowledge of astronomy was only copied from the 'sophisticated' cultures around about. On the contrary; not only was the Hebrew calendar superior to Egypt's wandering year, but it predated Meton by a thousand years. There was nothing anywhere else quite like it.

The Fiftieth Year

This brings us to the second synchronisation. In addition to the 'week', the Bible reveals a 49-year Sabbatic cycle starting New Year, 1st of Abib, following the previous block of forty-nine. They would have intercalated months as explained using the short cycle, until it reached the 7th month of the 49th year Then on the tenth day, a special 50th year was announced. This might seem strange but another astronomical formula is at work. The gap between the two events comes to 17718 days - a figure equaling exactly 600 lunar months. This gap never alters; it is always the same.


Now, 600 months equal 50 lunar years which explains why the Jubilee fiftieth year is superimposed over the other years. It takes 48½ solar years to equal 50 lunar years, so the 'overlaid' Jubilee is a device that equalises the solar and lunar cycles to 50 years each, after which the new cycle began afresh. Let us take another hypothetical example from modern times. If we say 1st Nisan AD 1950  was the start of a cycle and count to the 7th month of the 49th year, it comes to 1st Tishri AD 1998, and 17718 days. Here are the dates:


1st Nisan .................. to .................. 1st Tishri
(19th March) ..... = 17718 days ....... (21st September)
1950 AD .......................................... 1998 AD


This formula is very precise, and may be observed from ancient times until now. I am not suggesting that we should continue to observe the old system or festivals. I'm just noticing that the calendar formulas still work. They works just as well today as they did in biblical times! An information video on the fiftieth year may be found below.

In summary, the pre-Metonic Hebrew calendar was a 7-year cycle of alternating 86 / 87 months, crosschecked by a long cycle of 600 months over 50 lunar years, and 606 months over 49 solar years. Its distinguishing mark was a Sabbatical 'stamp' making it unique from every other national calendar.

See video on the fiftieth year.

(7 minutes)

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