As we can clearly see, the bible relates to a month as a 30 days period: 150 days of the flood which are five month (genesis 7,8), the feast of Ahasuerus of 180 days that are 6 months and so on. We also know that the moon dictated the beginnig of each month. So the are two options for calculations of year span: lunar (354 days) and 12 months of 30 days each (resulting in 360 days).

However, we know that the Israelites couldn't observe the feast in their yearly proper time by using of each of these calendars. But there is no mention in the bible of leap years as means of coping with the lack of days.

So, is there any historical explantion for this problem (considering the era before the arrival of the Sanhedrin and the Masoratic calculations)?

  • The Essenes had a 360 day year. Why do you say we know that they could not observe feasts at their proper time if the 360 day year always falls on the same day of the week each year? Commented Feb 15, 2019 at 2:30
  • It seems that the Essenes had a 364 days calendar: bibarch.com/concepts/calendrics/essene_calendar.htm Anyway, the solar year is a beat more than 365 days, so it can't be reconciled with a 360 days' calendar (or 364 days for that matter).
    – Elyoeinay
    Commented Feb 15, 2019 at 5:05
  • 1
    Wikipedia has an article about the current Hebrew system of a 19 year Metonic cycle and the addition of intercalary months which adjust between the solar year and the lunar year.
    – Nigel J
    Commented Feb 15, 2019 at 9:31
  • In Joshua chapter 10 God stopped the spin of the earth, and in Isaiah 38 He reversed it for a while. If God has this power I assume he could have sped up the earth's spin a bit to squeeze in 365 days in a year, instead of 360. Commented Feb 15, 2019 at 13:10
  • related: hermeneutics.stackexchange.com/questions/35457/…
    – bach
    Commented Feb 15, 2019 at 16:13

4 Answers 4


Sacha Stern in his book Calendar and Community: A History of the Jewish Calendar, 2nd Century BCE to 10th Century CE discusses this problem, and shows that the bible actually gives us contradictory clues regarding the reckoning of the biblical calendar.

Indeed "the flood" that the OP brings as evidence that the biblical year is lunar is used by the author, as well, as evidence that the biblical year is lunar, albeit in a different way:

Gen. 7-8 began on the 17th of the second month and ended on the 27th of the same month of the next year, thus lasting one year and 10 days. As pointed out already in rabbinic sources, these 10 days may represent the difference between the solar and the lunar year. This would suggest that the biblical calendar year was lunar, but that the Flood lasted the equivalent of one solar year. (Calendar and Community, p. 2)

But then the author goes on to prove from Num. 10 which according to its reckoning the Israelites resided at Sinai for one year minus ten days. This proves the exact opposite--that the biblical calendar year is usually solar and that on this occasion they resided at Sinai for the duration of a lunar year. You can read it here.

He also refutes those who support that the Israelites followed a lunar calendar from the fact that the bible uses the term Hodesh, since the new moon is implicit in the root HDSh. This is flawed according to the author since almost all solar calendars include monthly cycles of approximately 30 days each. This just means that the 30-day month originated from the monthly cycle of the moon, but that once it was adopted into the solar calendar it lost its functionality. The author himself concludes that the evidence from the bible is inconclusive, and that since the bible is reticent on this subject we cannot say with certainty what kind of calendar the Israelites followed.

As you can see, this problem is more complex than you might think. The fact that the bible usually reckons a month as the equivalent of 30 days does not prove ipso facto that the biblical calendar included a lunar reckoning that would have necessitated an intercalation or a leap year as you have it. It is totally feasible that the bible treats them merely as schematic cycles in which a perfect lunar month corresponds to 30 days, but that does not preclude a technique of using of defective months in real-life biblical calendars in order to ensure that the months keeps up with the solar or agricultural calendar which the Israelites used for their festivals and sabbaths. This process may have been similar to those used by the Gregorian and Julian calendars, in which lunar months are tailored to the solar calendar, yet they still retain their 30-day cycles on average. On the other hand, it is equally feasible that the biblical calendar followed both: the lunar and solar calendar and added an intercalary month to make up for the discrepancy as was done later during the Mishnaic period. All I'm saying is that the fact that bible uses hodesh as corresponding to 30 days freely is not evidence that the bible followed a lunar calendar.

Hope this helps.


Scripture covers a period of thousands of years, during which time there may well have been a number of ways (some of them local) of adjusting the calendar. We now have a system of leap years but that only began in 1752. Previous to that, there was a different system.

But to an agricultural people - and until about 1700, we were all agricultural people - what was easiest to observe was the new moon. One knows almost exactly, to one or two days, when there is a new moon so one can determine the passage of the months quite accurately without any specialist knowledge.

What matters is, When do I sow my crops ? When do I start ploughing up the ground ? When do I let the rams among the ewes ?

And these questions are answered by the seasons and by one's own agricultural knowledge.

The question of how to administrate the year so that people pay their taxes - annually - at the right time is really a question for the government, not the populace and there are various ways of doing it, for example by having an extra month here or there (called an intercalary month).

Sacrifices in Israel were timed by the day, by the week, by the month, or by the season. I cannot think of one that necessitates a solar calendar, myself.

It is not surprising that scripture is ambiguous about something that is not a constant matter.

  • 1
    1752 was when Britain switched from the Julian Calendar to the Gregorian calendar, which had been in use elsewhere for nearly 200 years. Both calendars have annual leap days. The Gregorian calendar simply dropped 3 leap years out of every 400 year period, to make it more accurate. But neither have anything to do with the Biblical Hebrew calendar, whose leap years add an extra month seven times every 19 years. Commented Feb 16, 2019 at 3:32

Is a standard 30 day month implied in Genesis 7 & 8 ?

Or is the beginning or end of the time of the counting being factored into the total with the lunations?

In other words, Gen 7:11 says: In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.

And in ending in Gen 8:3-4 it says: And the waters returned from off the earth continually: and after the end of the hundred and fifty days the waters were abated. And the ark rested in the seventh month, on the seventeenth day of the month, upon the mountains of Ararat.

The time from 2-17 till 7-17 counts day 17 twice, this means IF the 150 day count is from 2-17 to 7-17 the lunation period could be 149 days with counting the day 17 of both months to make 150 days.

Example: (Remembering this is a month starting on day 17 of the month): month 2 has 30 days, month 3 has 30 days, month 4 has 29 days, month 5 has 30 days and month 6 has 30 days arriving at 7-16 + the 17th = 150 days

The 5 month of 30 day lunations has been assessed by various investigators, but only 4 consecutive monthly lunations are suggested as possible by experts, nevertheless, the model I had listed above is definitely possible.

Furthermore, The lunar cycle as evidently used by Israel, is especially evident in the many places where the LXX translated the Hebrew word חדשׁ -cHoDeSh to νουμηνία - nou-menia, that is literally New Moon, you can't solarize it. See LXX Greek besides the Hebrew in Exodus 40:17 and Numbers 10:10 for some examples.

The lunar cycle has no set amount of days per year by observation, it can have only a 29 or 30 day month, this means that at certain times multiple months will have 29 days in a row and multiple months at times will have 30 day, as well they will interchange 29 then a 30 and so on., Thus, the number of 354 is an average and not absolute. However, while biblical months are lunar, the Biblical Calendar Year is only conveyed as Agricultural :

Exodus 12:2 This month shall be unto you the beginning of months: it shall be the first month of the year to you. Deuteronomy 16:1 Observe the month of Abib- אביב and keep the passover unto the LORD thy God: for in the month of Abib the LORD thy God brought thee forth out of Egypt by night.

Thus, it is the law of necessity that requires a 13 month epact about every 3 years in order to allow Abib, meaning barley in the ear, as seen in Exo 9:31 where the barley is here called Abib- אביב, to occur in the Month of Abib.


The Jews did not invent the wheel, they merely borrowed their calendar(s) from the two ancient civilizations of Egypt and Babylon.

Hope this helps.


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