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The Calculated Jewish Calendar vs. the Biblical Jewish Calendar

Updated: Oct 6, 2023

God commanded His Feast Days, His Moedim (appointed times), to be kept at the right time of each year beginning with Pesach (Passover), according to Deuteronomy 16:1. “Observe the month of Abib, and keep the Passover to the Lord your God, for in the month of Abib the Lord your God brought you out of Egypt by night. The children of Israel left Egypt after the 10th plague that God sent to convince Pharaoh and the Egyptians to let His people go.

However, the seventh plague is the indicator of what time of the year the Exodus occurred.

The seventh plague was when the LORD sent hail mixed with fire in all the land of Egypt, except in Goshen where the Hebrews were. Exodus 9 says that it was so very heavy that there was none like it in all the land of Egypt since it became a nation. “And the hail struck throughout the whole land of Egypt, all that was in the field, both man and beast; and the hail struck every herb of the field and broke every tree of the field” (Exodus 9:25).

We know Abib (now known as Nisan) occurred in the early spring because of the following verse: “Now the flax and the barley were struck, for the barley was in the head and the flax was in bud. But the wheat and the spelt were not struck, for they are late crops” (Exodus 9:31-32). The month of the exodus was the month of the “abib” crops, that is, the month of the year in which the crops were already known to begin to turn green each year.

The wheat, coming out of the ground later, was now tender, and hidden, either under the ground, or in the herb, whereby it was secured both from the fire, by its greenness and moisture, and from the hail, by its pliableness and yielding to it: whereas the stalks of barley were more dry and stiff, and therefore more liable to be injured and destroyed by the fire and hail. In Egypt, the wheat harvest is at least a month later than the barley harvest, coming in April, whereas the barley harvest is finished by the end of March.

Shortly after the seventh plague and before the tenth and final plague, God told Moses and Aaron, “This month shall be your beginning of months; it shall be the first month of the year to you”(Exodus 12:1). The LORD changed the “counting of months” from the first month of fall to the first month of spring so the 1st calendar month of the year would now coincide with the month of the Hebrew’s new-found freedom - the month of the exodus. However, the “counting of years” would remain with the original fall calendar (the civil calendar).

The LORD informed Moses and Aaron regarding the tenth and final plague, the Passover plague, in which He would kill all the firstborn (man and beast) of Egypt. The LORD instructed Moses and Aaron on how to avoid the same fate as the Egyptians with the blood of the Passover lamb. The first Passover (and all God’s instructions regarding it) and subsequent days of eating only unleavened bread for seven days are described in Exodus 12:1-29). In Deuteronomy 16:6, the LORD reiterated, “You shall sacrifice the Passover at twilight, at the going down of the sun, at the time you came out of Egypt.”

The original Hebrew calendar (like the Egyptians) began in the fall season when the last of the harvesting of crops occurred and the planting for the spring crops began. The sun (autumnal equinox) determined the season (moed) every year for this harvesting and planting, and the moon (new moon) determined when the months would begin on their calendar. At the original Passover, in 1446 BC, God changed the start of the Hebrew calendar so it would always be anchored to the Passover when the children of Israel came out of Egypt.

“Let the children of Israel also keep the passover at his appointed season. In the fourteenth day of this month, at even, you shall keep it in his appointed season: according to all the rites of it, and according to all the ceremonies thereof, shall you keep it” (Numbers 9:2-3). The appointed season was the beginning of spring. The sun still determined the season, as the first month of the calendar would always occur around the vernal equinox (spring) when the early barley crops were “abib.” The new moon would still begin the months, and approximately 14-15 days later, when the moon was completely full, the Passover would begin. Thus, Passover is tied to both the vernal equinox and the full moon.

However, you no longer watch for the day of the new moon to begin the year, instead, you assess which new moon establishes the proper day of the Passover to begin the annual remembrance! Therefore, the rule to determine the month of the abib crops (modern Nisan) is the new moon that establishes Passover on or after the Vernal Equinox.

This is the Biblical Hebrew calendar that was still in use in Jesus’ time. The moon was observed and not mathematically calculated. The crops were also observed for readiness to harvest. Regarding the original Passover in 1446 BC, according to AstroPixels - Moon Phases: -1499 to -1400, the new moon conjunction of Abib occurred on March 11, 1446, BC, Israel time, (with a total solar eclipse on that date) and the full moon of Passover would have been approximately 14 days later on March 25, 1446 BC.

After the Jews were forced out of the land of Israel in 135 AD and could no longer determine their calendars, as they couldn’t observe the heavenly signs from Jerusalem any longer (nor determine their crop’s readiness for harvest), they eventually developed a mathematically calculated calendar based on the 19 year Metonic (intercalation) cycle. This is known as the modern Jewish calendar and is still used today for religious purposes. It is quite ingenious but it is not as accurate as the ancient observed calendar, and has many flaws. Also, through the centuries, many rules have been added by the rabbinic Jews that are not biblical. Below are just a few of them:

  1. Pesach: The Passover, begins on 15 Nisan and lasts for seven days in Israel and eight days outside Israel. It can only begin on Monday, Tuesday, Thursday or Saturday.

  2. Shavuot: The Feast of Weeks, which falls on 6 Sivan or 7 Sivan outside Israel. It can only fall on Monday, Tuesday, Thursday or Sunday.

  3. Rosh Hashanah: The Jewish New Year, which falls on 1 Tishrei. It can only fall on Monday, Tuesday, Thursday or Saturday.

  4. Yom Kippur: The Day of Atonement, which falls on 10 Tishrei. It can only fall on Monday, Wednesday, Thursday or Saturday.

  5. Sukkot: The Feast of Tabernacles, which begins on 15 Tishrei and lasts for seven days. It can only begin on Monday, Wednesday, Friday or Saturday.

  6. Certain months are restricted to 29 days, while others are restricted to 30 days. A few of them can be either.

I always knew the calculated Jewish calendar could be off by a few days because of these rules, but I didn’t realize until recently that it might be off by a month from the astronomically Biblical calendar. I gathered the following information from 2022_Calendar.pdf (therefinersfire.org). I highly recommend this website as I now agree with their assessment on most things, including how to determine the first day of every month by the new moon conjunction and not the crescent moon.

“The modern, authoritative calendar of Israel applies the rigid but erred, Metonic cycle to their calendar, while the Biblical calendar only intercalates when Passover would naturally fall before the Vernal Equinox. We have seen in recent years that the modern, Calculated calendar of Judaism is more and more divergent from the real sun, moon, and stars. In some years, the date of Passover and all commanded moedim as determined by the authorized calendar fall in the wrong lunar month. 2016 and 2019 are examples. And it will happen again in 2024, 2027, 2030, 2035, and 2038.”

“We strive to provide a calendar that most closely resembles the calendar alluded to in scripture while holding true to the real sun, moon, and stars. The rules for our calendar are summarized as follows:


  1. The 1st day of any new Hebrew month is the sunset which follows the observed conjunction of the moon. Calculating the time of conjunction and comparing that with the time of sunset (in Jerusalem) matches what the ancient Levite observers could have done by watching the signs of the old crescent at the end of each month (Note: See the website linked above for how this is possible).

  2. The 1st month of the ecclesiastic calendar year is the new moon which establishes Passover (the afternoon of the 14th of Nisan), on or after the Vernal Equinox. This is the same as saying the 1st month is the new moon closest to the Vernal Equinox (whether the new moon is before or after the Vernal Equinox). No other rules are added. All the designated feasts, the moedim (appointed times, Leviticus 23), fall on the calendar days they fall on. If Yom Kippur is on a Friday or a Sunday, then that’s when it is. If the 7th day of Sukkot falls on a Saturday, then so be it. No artificial “postponements” for convenience are imposed.”

According to the Refiners Fire website (see link above), here are a few more problems with the modern calculated Hebrew calendar: “The current Hebrew calendar calculates the first day of each new month using an “average moon” instead of the real moon. That is, the lunation is fixed to approximately 29.53 days, while the lunation of the actual moon varies from a low of 29.27 to a high 29.84 days. The result is that the traditional calendar sometimes declares the 1st of the calendar month when the moon clearly has not yet reached conjunction and thus has not been “renewed” or declares the first day of the new month a day after the moon has been renewed. Thus, the traditional calendar month sometimes begins a day too early and often it begins the month a day too late.

This is very important, the determination of the new moon establishing the critical 1st month of each year is determined by the fixed application of the Metonic cycle, where the required periodic leap month is added by a fixed schedule of intercalation – completely ignoring the real moon! This sometimes causes the wrong new moon to be identified as the “1st month”, the month of Nisan. This error, when it happens, establishes ALL COMMANDED FEAST DAYS following Nisan to be observed in the wrong lunar month!

This error is occurring more and more often in the modern Hebrew calendar as the centuries progress. This problem is well recognized, even in modern Judaism. Applying the Metonic cycle to the Hebrew calendar is perfectly fine over the whole 19-year cycle, but it is dreadfully wrong to apply the “rules” of the Metonic cycle by its rigid schedule of intercalation within any 19-year period. The actual moon should declare which year should be the intercalary year, not a rigid, predetermined schedule!

Finally, the modern Hebrew calendar assumes the Vernal Equinox is the 25th of March – the date of the Vernal Equinox during the Julian calendar era in 45 BCE. But the Vernal Equinox since 1582 CE has always fallen between March 19th and March 21st by the Gregorian calendar which was established that same year, 45 BCE. Thus the modern Hebrew calendar ignores the actual Vernal Equinox, which contributes to the incorrect month chosen as Nisan in certain years.”

So, why does all of this matter? Well, for one thing, if the Jews still had a temple and the High Priest went into the Holy of Holies on a day that wasn’t truly Yom Kippur (the day of Atonement), he would be killed by God! Also, if the Lord Jesus fulfilled the first four Feasts of the Lord during His first advent on the appointed days of the Moedim, shouldn’t He do likewise with the remaining three Feasts during His second advent? It would be nice to know the appropriate dates and months for the fall Feasts of the Lord.

Although we don’t know which year Jesus is to return, we can look at future calendars (that are determined by the biblical, and astronomically correct calendar) and see what dates the three remaining Feasts of the Lord occur on in any particular year. We know He can’t return until the seven-year Tribulation (Daniel’s 70th seven) is over, and we know by the convergence of signs the Tribulation is not too far off.

We can also look back in time to determine the most likely and astronomically correct dates and (the day of the week) of the new moon of Nisan and Passover during Jesus’ last year, according to biblical and historical data. We should be able to determine the date and day of the death, resurrection, and ascension of Jesus, and the subsequent giving of the Holy Spirit on Pentecost.

So, with all this in mind, let’s compare the Calculated Jewish calendar with the Biblical calendar that more resembles the ancient observed (astronomical and agricultural) calendar. Let’s look at some 21st-century dates for Nisan 1 for both calendars for a complete Metonic cycle of 19 years and compare them. Regarding the Calculated Jewish calendar, the first of every month (and when to add an extra month) will be determined by a pre-determined mathematical formula.

Regarding the Biblical Jewish calendar, the first of every month will be determined by the conjunction of the new moon. Nisan 1 will occur 1 day later. An intercalary month will be added if the first full moon of spring occurs before the vernal equinox (March 20 in the Northern Hemisphere for our dates). The lunar year for these calendars must have at least 353 days in a year, and if an intercalary year is added no more than 385 days per year.

NISAN 1 DATE FOR BIBLICAL JEWISH CALENDAR

NISAN 1 DATE FOR CALCULATED JEWISH CALENDAR

March 7, 2019 – March 24, 2020 (384 days)

April 5, 2019 – March 24, 2020 (355 days)

March 25, 2020 – March 13, 2021 (354 days)

March 25, 2020 – March 12, 2021 (353 days)

March 14, 2021 – April 1, 2022 (384 days)

March 13, 2021 – March 31, 2022 (384 days)

April 2, 2022 – March 21, 2023 (354 days)

April 1, 2022 – March 22, 2023 (356 days)

March 22, 2023 – March 10, 2024 (355 days)

March 23, 2023 – April 7, 2024 (382 days)

March 11, 2024 – March 29, 2025 (384 days)

April 8, 2024 – March 28, 2025 (355 days)

March 30, 2025 – March 19, 2026 (355 days)

March 29, 2025 – March 18, 2026 (355 days)

March 20, 2026 – March 8, 2027 (354 days)

March 19, 2026 – April 6, 2027 (384 days)

March 9, 2027 – March 26, 2028 (384 days)

April 7, 2027 – March 27, 2028 (356 days)

March 27, 2028 – March 15, 2029 (354 days)

March 28, 2028 – March 15, 2029 (353 days)

March 16, 2029 – March 4, 2030 (354 days)

March 16, 2029 – April 2, 2030 (383 days)

March 5, 2030 – March 23, 2031 (384 days)

April 3, 2030 – March 23, 2031 (355 days)

March 24, 2031 – March 11, 2032 (354 days)

March 24, 2031 – March 11, 2032 (354 days)

March 12, 2032 – March 30, 2033 (384 days)

March 12, 2032 – March 29, 2033 (383 days)

March 31, 2033 – March 20, 2034 (355 days)

March 30, 2033 – March 19, 2034 (355 days)

March 21, 2034 – March 10, 2035 (355 days)

March 20, 2034 – April 8, 2035 (385 days)

March 11, 2035 – March 27, 2036 (383 days)

April 9, 2035 – March 27, 2036 (354 days)

March 28, 2036 – March 17, 2037 (355 days)

March 28, 2036 – March 15, 2037 (353 days)

March 18, 2037 – March 6, 2038 (354 days)

March 16, 2037 – April 4, 2038 (385 days)

March 7, 2038

April 5, 2038

Out of 19 years, there is only 1 year with the exact same dates. There are only 9 years that have the same amount of days (within a few days). They have the same amount of months (either 12-12 or 13-13) The remaining 9 years are 30 days or so apart. They have a different amount of months (12-13 or 13-12). In other words, only 10 out of 19 years have matching intercalary months. Out of 19 years, both calendars have 6940 days, which is the same as the Gregorian calendar. After 19 years, the start of the next year matches the date of the start of the 19-year cycle for both calendars.

Evidently one of these calendars is not correct. You can tell just by looking at them, which one it is. Look how uniform the Biblical calendar is. There is only one year that begins in April, and it is only two days into April. All the rest of the years (18 years) begin in March. Now, look at the calculated calendar. There are six years that begin in April, and one of them is as late as April 9th (2035). That would put Passover on April 22 for that year, which is more than a month after the vernal equinox.

Regarding the full moon conjunction phase (99.9-100% of the moon is illuminated) of Passover for the 2019-2038 Metonic cycle, here are the results for the Biblical Jewish calendar: There are 7 full moons on the 14th day of Nisan, 10 full moons on the 15th day of Nisan, and only 2 full moons on the 16th day of Nisan. Generally, the full moons should occur on Nisan 14 or 15. Every once in a while they will occur on Nisan 16.

Here are the results for the Calculated Jewish calendar: There are only 3 full moons on the 14th day of Nisan, 6 full moons on the 15th day, 9 full moons on the 16th day, and 1 full moon on the 17th day. It appears the full moon of Passover is coming too late and too often on the calculated calendar. I believe the intercalary month is being added in the wrong year (in some years), placing the next year’s Passover Feast (and subsequent moedims) a month too late. If the first month of Abib/Nisan were to begin one month too late, then the too-ripe barley grains would fall to the ground and the harvest of the firstfruit sheaf would no longer be possible.

If the Calculated Jewish calendar is not the correct calendar that should be in place, then that means the Jews have been celebrating their Feast days in the wrong months for almost half of the years since they were back in the land in 1948. These two calendars with differing dates for new moons and Feast days pose a problem for Jews in the upcoming years. Without a Sanhedrin council in place, the calendar cannot be changed. I would imagine once they decide to build a new Temple in Jerusalem, there will have to be a Sanhedrin council established, but it remains to be seen if they will change their Calculated Jewish calendar.

Let’s look at the upcoming year of 2024, and I will show you what I mean. Regarding the Calculated Jewish calendar, the Passover Feast, including Unleavened Bread, will take place from April 21-28. The counting of the Omer begins on April 23 and ends on June 11/12 on Shavuot (the rabbinic Jews and the Pharisees of old believe the counting of the Omer of Leviticus 23:15 begins on Nisan 16). Rosh Hashana will take place on October 3. Yom Kippur will take place on October 12. Sukkot will take place on October 17-24.

Regarding the Biblical Jewish calendar for 2024, the Passover Feast will take place from March 24-31 (with the Feast of Firstfruits on March 31). Shavuot/Pentecost will take place 49 days past the Sunday after Passover (this is my interpretation of Leviticus 23:15 as well as the Karaite Jews, and the Sadducees of old) on May 19. Rosh Hashanah will take place on September 4. Yom Kippur will take place on September 13. Sukkot will take place on September 18-25. All of these moedim take place one month earlier than that of the Calculated Jewish calendar.

EASTER, GOOD FRIDAY, AND PENTECOST

Easter usually agrees with the Biblical Jewish calendar’s Feast of Firstfruits but not always. How is Easter determined? I’m glad you asked. Here’s how timeanddate.com explains it. “Easter falls on the first Sunday after the Full Moon date, based on mathematical calculations, that falls on or after March 21 (Western Christianity uses the Gregorian calendar dates). If the Full Moon is on a Sunday, Easter is celebrated on the following Sunday.

Although Easter is liturgically related to the beginning of spring in the Northern Hemisphere (March equinox) and the Full Moon, its date is not based on the actual astronomical date of either event. March 21 is the Church’s date of the March equinox, regardless of the time zone, while the actual date of the equinox varies between March 19 and March 22, and the date depends on the time zone.

The date of the Paschal Full Moon, used to determine the date of Easter, is based on mathematical approximations following a 19-year cycle called the Metonic cycle. Both dates may coincide with the dates of the astronomical events, but in some years, they don’t. For example, in 2019, the March equinox in the Western Hemisphere happened on Wednesday, March 20, while the first Full Moon in spring was on Thursday, March 21 in many time zones.

If the Church followed the timing of these astronomical events, Easter would have been celebrated on March 24, the Sunday after the Full Moon on March 21. However, the Full Moon date in March specified by the Church’s lunar calendar, also called the ecclesiastical Full Moon, was March 20, 2019 – one day before the ecclesiastical date of the March equinox, March 21. For that reason, the Easter date 2019 was based on the next ecclesiastical Full Moon, on April 18. This is why Easter Sunday 2019 was on April 21.”

The same type of anomaly occurs again in 2030 and 2038. These are years that have an intercalary month added at the end of the Calculated Jewish calendar (whereas the Biblical calendar does not). In 2030, the full moon of March comes on March 19, two days earlier than the stipulated date for the Church’s March equinox of March 21, so Easter is delayed until April. The first full moon of April 2030 is on Thursday, April 18, so Easter is three days later on Sunday, April 21, 2030. Basically, the same situation occurs in 2038, where Easter is in April (April 25).

In these particular three years of this Metonic cycle, Easter comes a few days after Passover on the Calculated Jewish calendar, but they follow the Sadducees’ and Karaite’s reckoning of determining Firstfruits (the day after the weekly Sabbath after Passover).

For the remaining 16 years of this Metonic cycle, when the two calendars agree on the same intercalary month reckoning, Easter will occur on the Sunday following Nisan 14 for both calendars.

When the two calendars are not in agreement on the same intercalary month reckoning, Easter will follow the Biblical Jewish calendar’s reckoning (except for 2019, 2030, 2038). Easter aligns with the Biblical calendar’s dates for Firstfruits for 16 out of 19 years for this Metonic cycle. I don’t know why the antiquated rules for determining Easter should still be in place and why the Church can’t just follow the Biblical Jewish calendar dates for the Feast of Firstfruits regarding Resurrection Sunday.

Easter determines when Good Friday is (two days earlier) and what date Pentecost will be on (49 days from Easter). If you get the date of Easter wrong, you will get Good Friday and Pentecost wrong as well. Of course, I have never believed Christ was crucified on a Friday because it is mathematically impossible to get three days and three nights from Friday to Sunday. I have always believed the crucifixion was on a Thursday. I believe the only day of the week for a Thursday crucifixion is 33 AD.

As a matter of fact, if you look at the possible years of the crucifixion (29 – 34 AD) and reckon Nisan 1 by the rule of the Biblical Jewish calendar (where Nisan 1 comes the day after the conjunction of the new moon, Israel time) here are the results for the day of the week for Passover, Nisan 14:


29 AD – Saturday, April 16

30 AD – Wednesday, April 5

31 AD – Monday, March 26

32 AD – Sunday, April 13

33 AD – Thursday, April 2

34 AD – Tuesday, March 23

As I am writing this article in 2023, we are currently in the time of the yearly seventh Feast of the Lord known as the Feast of Tabernacles, or Sukkot. Both calendars are in agreement on the timing of this Feast. The next feast of the Lord will come in the spring of 2024 during the time of Passover, or Pesach. The Passover, according to the Bible, occurs on Nisan 14 and the Feast of Unleavened Bread is from Nisan 15 to Nisan 21. However, the Jews have combined them (more or less) and Passover is from Nisan 15 to Nisan 21, with Nisan 14 being the day of Preparation (or the Passover offering).

The Jews now call the Feast of Firstfruits (a.k.a. wave sheaf offering) the start of the “counting of the Omer,” which ends on Shavuot. As I mentioned before, the rabbinic Jews believe the counting begins the day after the “special” sabbath (Nisan 15) on Nisan 16. So, on the Jewish Calculated calendar, the day of Shavuot will be on Nisan 6, every year (as long as it comes on Monday, Tuesday, Thursday, or Sunday). I find this to be unbiblical in more than one way.

In my article, The End of the Age – From Firstfruits to Hanukkah: Part II (rev310.net), I gave several potential (hypothetical) dates for Jacob’s Trouble (a.k.a. Daniel’s 70th week) based on the Abomination of Desolation occurring in the midst of the seven years (during the Passover Feast) and Jesus returning at the end of the Tribulation and fulfilling the last three fall Feasts of the Lord (Trumpets, Atonement, and Tabernacles). These dates were based on the Calculated Jewish calendar and the years that intercalary months were added accordingly.


In my next article, we will re-examine these calculations in light of the new empirical evidence (dating method) that the Biblical Jewish calendar contains, which I believe more closely resembles the original observed calendar of the Jews. We will also examine the Feast of Pentecost (Shavuot to the Jews) to see why many prophecy “experts” believe it is a high-watch day for the Rapture.

Randy Nettles

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