Nowadays, since the exodus, we have the Beis Din occasionally add a leap month to keep Nissan in Chodosh haaviv, or at least rely on the set calendar.

What did people do in the beginning of creation up until the exodus?

If they didn’t add a month then then how did the calendar still keep pesach in the spring? (And if it fluctuated, then did the first Pesach just happen to be in the spring)?

I want to try to calculate the number of milliseconds that has passed since 25 Elul year -1 (or is that year 0 from 5784?), or at least see if it’s possible.

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    Our calendar is based off the assumption that it was always fixed exactly like it is now. If your goal is just what you wrote in the last paragraph, then the rest of your question is irrelevant to that aim.
    – magicker72
    Commented Sep 28, 2023 at 18:53
  • @magicker72 what do you mean? It’s fixed since we have no Beis din now, and a fixed calendar was established. The question is if it’s possible to mathematically calculate backwards or if it’s all dependent on the beis din that we have no records of Commented Sep 28, 2023 at 20:28
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    I mean that the calculation of Tishrei 1 of year 5784 requires the (counterfactual) assumption that it's always been fixed.
    – magicker72
    Commented Sep 28, 2023 at 21:57
  • @magicker72 what do you mean? Trying to understand. We can calculate backwards the years, but in the times the Beis din calculated it there were sometimes extra months or extra days, is it Still possible to calculate the exact number of days since creation? If it was fixed before then maybe we could Commented Sep 28, 2023 at 23:03
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    @Dude hi. I mean the year it did occur not before “you are leaving in the chodesh haaviv..”. Also I don’t know it was in the spring before, it’s just an observation and part of the question. At least the first Pesach was in the spring, so if it fluctuated until the acidic then it would have had to be a pretty major coincidence that it happened to be so when it happened Commented Oct 2, 2023 at 2:22

3 Answers 3


Pirkei d'Rabbi Eliezer 8 says that adding leap years was originally done by Hashem, then handed over to Adam, from him to Chanoch, etc., down to the Avos and then to Yosef, and then "after Yosef and his brothers died, leap years were diminished among the Jewish people" and Hashem took the job back, until He handed it over to Moshe and Aharon.

ועיבורין היו לפני הקב"ה והיה מעבר את השנה ואחר כך מסרן לאדם הראשון בגן עדן... אדם מסר לחנוך ונכנס בסוד העיבור ועיבר את השנה... וחנוך מסר לנח סוד העיבור ועיבר את השנה... יעקב מסר ליוסף ונכנס בסוד העיבור ועיבר את השנה במצרים מת יוסף ואחיו נתמעטו העיבורין מישראל... מהו לאמור אמור להם לישראל עד עכשיו אצלי היה סוד העיבור, מכאן ואילך שלכם הוא לעבר את השנה.


It seems that the Babylonians already practiced a very similar calendar to ours. Being that Avraham came from that area, it could be we all followed it.

See this article from Wikipedia


1). The calendar system is accepted as a tradition and so presumably is the "calendar" system that was used before Hashem turned over the calendar to Chazal to mkadesh.

2). According to the Avudraham this is the correct system for determining leap years at all times. (I need a source, quickly skimmed and couldn't find it, I never read it, but heard it in his name).

3). We make Birkat HaChama when the sun returns to its "original" location during creation. Though this might just mean the specific hour on Tuesday I am sure there are opinions who are more astronomically minded. If so, it presumes a 19 year cycle from creation - otherwise there would be drift.

4). Molad is calculated based off of the previous new moon... so even if the first molad was given as Nissan in Egypt, you can just work backwards.

5). To know the exact millisecond would likely be impossible no matter what system since there were events like Hashem stopping the sun for Yehoshua. Unless you believe all these acts balanced out perfectly (like perhaps setting quicker by Yaakov). I can see this as a matter of debate.


Your question seems to depend on adding two Adars. If Chazal added an "extra" month too many, they would need to remove a month in the future otherwise things would not be balanced. So things would even out. At best, it could be a "month" off, giving you a few possibilities.

Similarly the Gemara (Rosh Hashana (10b)) has a Machlokes if the world was created in Tishrei/Nissan and when the Avos were born etc... This imo presumes that the calendar was operative otherwise I don't particularly understand the machlokes. It would imo mean our Nissan and Tishrei. To disagree, one would need to argue, that the date doesn't matter, but the metaphysical month, which I suppose is possible.

In a different point, the Ramban points out that Tishrei overlaps with the symbol of the weights/measure in astrology. Something that was passed down even among non-Jews, that this is a time of judgement. It would appear that Tishrei was always at this time. (Drasha Rosh Hashana)

In a similar vein that the Chafetz Chaim (Shem Olam Chelek Aleph Perek Gimmel) (and Ramban above) points out that the Sheep/Goat/Ram is the month of Nissan at the time when the Egyptians worshiped their deity. At that time we took their idol and slaughtered it in its month when the moon was full (precisely chazot).

Now perhaps you could argue that it happened that hebrew year just "happened" to realign with the summer (non-Jewish) and astrological calendar. I suppose this is possible, but not once again Pashut Pshat.

It would appear to me that the Calendar existed with leap months.

  • I do need the millisecond. The question is if it’s possible to get the exact number of days because sometimes the Beis din added a month etc Commented Oct 2, 2023 at 23:14
  • @YaakovYitzchakbenMoshe Ok - I have edited the answer to be more clear that it is this calculation or nothing, and the reasons to rely on it.
    – msj121
    Commented Oct 3, 2023 at 11:53
  • Thanks. I’m having trouble understanding it though. If a beis din added a month let’s say in year 3000, then wouldn’t that add 30 days to that year that we would know about? Also even if the sun stopped did that add a day to the calendar itself? Commented Oct 3, 2023 at 14:05
  • @YaakovYitzchakbenMoshe, this is all backwards. The current calendar was established less than two thousand years ago. Everything prior to then is just backwards calculation, for sake of convenience in our current calculations, nothing more. Before that the Beis Din kept things in good order. Before the Torah was given, I don't know what anyone did. If Avraham Avinu "kept the Torah before it was given" he must have made his own decisions as a Beis Din.
    – MichoelR
    Commented Oct 3, 2023 at 15:29
  • @YaakovYitzchakbenMoshe updated
    – msj121
    Commented Oct 3, 2023 at 16:30

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