Adar II – The Thirteenth Month

This year, 5782 on the Hebrew calendar coinciding with 2021-22 on the Gregorian Calendar, is a “leap” year. We are adding an additional month, unlike the Gregorian calendar that adds an additional day during leap years. What is the purpose behind the thirteenth month of Adar II? Is it ever mentioned in the Bible?

The calendar can be a very divisive subject in the Messianic and Hebrew Roots community. The Bible does not give us explicit instructions, leaving us sometimes to either rely on tradition or to use deductive reasoning to come up with some sort of application for what is explicitly said. For example:

Now the LORD said to Moses and Aaron in the land of Egypt, “This month shall be the beginning of months for you; it is to be the first month of the year to you.”
(Exodus 12:1-2)

We know from surrounding context that “this month” (Hebrew: hachodesh hazeh) is the month of Abib (Exodus 13:4) – sort of, and I will address that later. However, “month” is not defined. We know, or think we know, what a month is by tradition and reasoning. The same goes for “year.” And how, from the Bible, do we know when it is “this month?” Many of us think we know the answer, and yet we will disagree.

The Moon and The Sun

The Hebrew (Jewish) calendar is a luni-solar calendar, meaning it is based on both the moon and the sun. Many believe this is the Biblical calendar, or very close to it, others will contend it is not.1 But for the remainder of this post, this is the calendar we will consider.

Then God said, “Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years; and let them be for lights in the expanse of the heavens to give light on the earth”; and it was so. God made the two great lights, the greater light to govern the day, and the lesser light to govern the night; He made the stars also.
(Genesis 1:14-16)

Using both the sun and the moon as described in these passages, we can define a couple of terms.

A lunar month is the time it takes for the moon to orbit the earth. Specifically, the moon’s orbit around the earth takes 29 days, 12 hours, and 44 minutes. We could go into more detail counting to fractions of a second and considering the simultaneous rotation of the earth and the earth’s orbit around the sun, but that serves no useful purpose here. We’ll just call it 29-1/2 days. And since we need to consider a lunar month being to be made up of full days, the Hebrew calendar alternates between 29-day and 30-day months.

A solar year is the time it takes for the earth to orbit the sun. Specifically, that is 365 days, 5 hours, and 48 minutes (and 46 seconds). We’ll just call it 365-1/4 days. And for a solar year made up of full days, we have three years of 365 days and then one year of 366 days. Usually – it still takes some refinement every 400 years or so.

So here is the problem: 12 lunar months averaging 29-1/5 days is 354 days. We are short 11-1/4 days of a full solar year. With a twelve-month year, it wouldn’t take long for the first month to be in the winter, and it would keep moving up by 11 days every year.2 We can’t add extra days to the month and stay in sync with the moon, so to keep the months aligned with the proper season, we add an extra 29- or 30-day month approximately every three years. It’s actually 7 times in a cycle of 19 years.

The stars (constellations) confirm the solar year, and the “signs of the zodiac” are based on twelve solar months not related to the moon.

Are the Months Named in the Bible?

Typically, the months of the year are simply called the first month, second month, third month, etc. in the Bible. There are a few exceptions. Here are the months and their modern names along with their Biblical name when applicable.

First Month Nisan Aviv/Abib
Exodus 13:4; 23:15; 34:18; Deuteronomy 16:1
Nehemiah 2:1
Second Month Iyyar
Third Month Sivan Sivan Esther 8:9; Baruch 1:8
Fourth Month Tamuz
Fifth Month Av
Sixth Month Elul Elul Nehemiah 6:15; 1 Maccabees 14:27
Seventh Month Tishrei Ethanim 1 Kings 8:2
Eighth Month Cheshvan Bul 1 Kings 6:38
Ninth Month Kislev Chislev Nehemiah 1:1; Zechariah 7:1
Tenth Month Tevet Tebeth Esther 2:16
Eleventh Month Shevat Shebat Zechariah 1:7; 1 Maccabees 16:14
Twelfth Month Adar Adar Esther 3:7,13; 8:12; 9:1,15,17,19,21


The first month is called Abib (or Aviv) in the Torah – Exodus 13:4; 23:15; 34:18 and Deuteronomy 16:1. None of the other months are given a name in the Torah, the first five books of the Bible. Specifically, this month is called chodesh ha-aviv, or “the new moon [month] of the aviv.” It is not clear whether aviv (or abib) is actually the name of the month or simply a description indicating the month when aviv (usually thought to be green ears of barley) appears.

The Thirteenth Month

All twelve months are mentioned in Scripture, some by name and all by number. However, there is no mention of a thirteenth month either by name or number. There are never any instructions to delay the start of the year for this or that reason, including the outcome of a barley search (which also is never mentioned). Did the ancient Israelites add a thirteenth month to keep the seasons aligned? If so, how did they know when to add one?

Based strictly on Scripture, those questions cannot be answered. Instead, we must rely on tradition, history, and maybe a little interpretive deduction. I haven’t been able to determine when intercalation, the use of a thirteenth month to keep the seasons aligned, was first used. No doubt it was already in use before any formal record of it can be found.

One passage in Ezekiel may allude to a thirteenth month even though it is not specifically mentioned.

Now it came about in the thirtieth year, on the fifth day of the fourth month, while I was by the river Chebar among the exiles, the heavens were opened and I saw visions of God. (On the fifth of the month in the fifth year of King Jehoiachin’s exile, the word of the LORD came expressly to Ezekiel the priest, son of Buzi, in the land of the Chaldeans by the river Chebar; and there the hand of the LORD came upon him.)
(Ezekiel 1:1-3)

Seven days later, which would be the 12th day of the month, Ezekiel receives this instruction:

At the end of seven days the word of the LORD came to me, saying…
(Ezekiel 3:16)

“As for you, lie down on your left side and lay the iniquity of the house of Israel on it; you shall bear their iniquity for the number of days that you lie on it. For I have assigned you a number of days corresponding to the years of their iniquity, three hundred and ninety days; thus you shall bear the iniquity of the house of Israel. When you have completed these, you shall lie down a second time, but on your right side and bear the iniquity of the house of Judah; I have assigned it to you for forty days, a day for each year.”
(Ezekiel 4:4-6)

As a part of what appears to be this initial vision, Ezekiel is instructed to lie on his side for a total of 430 days. He is to lie on his left side 390 days and then on his right side 40 days. The next time a date is mentioned in Ezekiel, he is sitting in his house with the elders of Judah.

It came about in the sixth year, on the fifth day of the sixth month, as I was sitting in my house with the elders of Judah sitting before me, that the hand of the Lord GOD fell on me there.
(Ezekiel 8:1)

If Ezekiel began lying on his side immediately after receiving the instruction on the 12th day of the 4th month of the 5th year of exile, and he is sitting up in his house on the 5th day of the 6th month of the 6th year of exile, we could assume that the 430 days has now passed.

If the year was 354 days long (12 months averaging 29.5 days) then the time between the initial prophecy which included lying on his side and the second prophecy that took place while he was sitting in his house would be: 354 days (one year) plus 53 days (from the 12th day of the 4th month to the 5th day of the 6th month) totaling 407 days. That isn’t enough time; Ezekiel should still be laying on his side.

But if it was a thirteen-month year consisting of 384 days, then we have 384 days (one year) plus 53 days. In total, 439 days have passed. Ezekiel has finished the days of laying on his side and is now seated with the elders of Judah.

When Is Purim?

Then Mordecai recorded these events, and he sent letters to all the Jews who were in all the provinces of King Ahasuerus, both near and far, obliging them to celebrate the fourteenth day of the month Adar, and the fifteenth day of the same month, annually… Therefore they called these days Purim after the name of Pur. And because of the instructions in this letter, both what they had seen in this regard and what had happened to them, the Jews established and made a custom for themselves and for their descendants and for all those who allied themselves with them, so that they would not fail to celebrate these two days according to their regulation and according to their appointed time annually.
(Esther 9:20-21,26-27)

Purim, according to the book of Esther, is on the 14th and 15th of Adar. But when a thirteenth month is added to the year, the twelfth month is designated as Adar I and the thirteenth as Adar II. According to Jewish tradition (as this is not a commanded feast of Yah), Purim is celebrated during the last month of the festival year – either Adar I or Adar II.

An Agriculturally Based Calendar

The Biblical festivals are based on an agricultural cycle. Passover is in the Spring of the year, and Shavuot is at the time of the early wheat harvest. Sukkot is a harvest festival at the end, or turn, of the year (Exodus 34:22). It order to keep the lunar months aligned with the proper season, it is necessary to occasionally add an extra month. Scripture does not tell us how or when to do that.

I have known of groups who determine when the year starts by the maturity of barley in Israel. I have known of others who base it on the equinox. There have been years when my friends were celebrating Biblical festivals a month ahead or a month behind the rest of us. This only leads to confusion.

The Hillel calendar used by the Jewish community keeps the festivals aligned with the seasons by adding a thirteenth month, Adar II, on a calculated cycle. Is it Biblical? Well, it isn’t un-biblical. And it’s the best method we have at the moment “for brothers to dwell together in unity” (Psalm 133:1).

Unless marked otherwise, Scripture quotations are from the New American Standard Bible (NASB) © The Lockman Foundation

1 Other calendars used by some groups are derived from literature such as the books of Enoch and Jubilees. The use of lunar months and the intercalation of a thirteenth month are not relevant to these solar-based calendar systems.

2. The Islamic calendar illustrates this problem. Their festival celebrations move up by approximately 11 days every year in relation to the Gregorian calendar.

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