I looked on the Hebcal website to see when the Erev Pesach will occur in the future (and also looked at the past), but found out that it's never a thursdag or sunday, did the Erev Pesach ever was or will be on those days according to todays calendars?

The same applies for other chagim that don't occur on specific days. Could someone explain me why?

1 Answer 1


The current fixed calendar is arranged (by adding or taking out an extra day in Marcheshvan or Kislev) such that Yom Kippur can't fall on Friday or Sunday (so there won't be two days in a row where no work at all can be done) and such that Hoshana Rabba can't fall on Shabbat. Most months are of fixed length, so this effectively limits all holidays in some ways. The dates that holidays cannot fall on (where 1 is Sunday, 2 is Monday, etc.) are (based on Shulchan Arukh OC 428:1): Rosh HaShana/Sukkot 146; Yom Kippur 316; Chanukka 3; Purim 247; Pesach/Tisha B'Av 246; Shavuot 357.

More specifically, Rosh Chodesh for each month can only be on certain days: Nisan 1357; Iyar 2357; Sivan 1346; Tamuz 1356; Av 2467; Elul 1246; Tishrei 2357; Marcheshvan 2457; Kislev 123456; Tevet 12346; Shevat 23457; Adar I 2457; Adar II 2467.

  • The reasoning behind this limitation is explained in Talmud Rosh Hashanna (I think it's approx. p. 20) regarding the concern of not having Yom Kippur on Friday or Sunday. Regarding Hoshannah Rabba, this is mentioned in Talmud Succah (don't recall exact page.) It's fascinating to note that the minhag of beating Hoshannot was considered more important than a possible concern of not hearing Shofar blown on Rosh Hashanna. (I have to inspect the history of that prohibition.)
    – DanF
    Commented Jun 17, 2019 at 21:08

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