Editing Hebrew calendar (section)

====Days of week of holidays====
{{Main|Days of week on Hebrew calendar}}

Jewish holidays can only fall on the weekdays shown in the following table:

{| class="wikitable"
|-style="background-color:#DDDDDD;text-align:center;"
|-
![[Purim]]
![[Passover]]<br />(first day)
![[Shavuot]]<br />(first day)
![[Seventeenth of Tamuz|17 Tammuz]]/<br />[[Tisha B'Av]]
![[Rosh Hashanah]]/<br />[[Sukkot]]/<br />[[Shmini Atzeret]]<br />(first day)
![[Yom Kippur]]
![[Chanukah]]<br />(first day)
![[Tenth of Tevet|10 Tevet]]
![[Tu Bishvat]]
![[Purim|Purim Katan]]<br />(only in leap years)
|-
|Thu||Sat||Sun||Sun*||Mon||Wed
|Sun or Mon
|Sun or Tue
|Sat or Mon
|Sun or Tue
|-
|Fri||Sun||Mon||Sun||Tue||Thu||Mon||Tue||Mon||Tue
|-
|Sun||Tue||Wed||Tue||Thu||Sat
|Wed or Thu
|Wed, Thu, or Fri
|Tue, Wed, or Thu
|Wed or Fri
|-
|Tue||Thu||Fri||Thu||Sat||Mon
|Fri or Sat
|Fri or Sun
|Thu or Sat
|Fri or Sun
|-
|colspan=10| <small>*Postponed from Shabbat</small>
|}

The period from 1 [[Adar]] (or [[Adar II]], in leap years) to 29 [[Marcheshvan]] contains all of the festivals specified in the Bible ([[Purim]], [[Passover]], [[Shavuot]], [[Rosh Hashanah]], [[Yom Kippur]], [[Sukkot]], and [[Shemini Atzeret]]). The lengths of months in this period are fixed, meaning that the day of week of Passover dictates the day of week of the other Biblical holidays. However, the lengths of the months of Marcheshvan and Kislev can each vary by a day (due to the [[#Rosh Hashanah postponement rules|Rosh Hashanah postponement rules]] which are used to adjust the year length). As a result, the holidays falling after Marcheshvan (starting with Chanukah) can fall on multiple days for a given row of the table.

A common mnemonic is "{{lang|he|לא אד"ו ראש, ולא בד"ו פסח}}", meaning: "Rosh HaShana cannot be on Sunday, Wednesday or Friday, and Passover cannot be on Monday, Wednesday or Friday" with each day's numerical equivalent, in [[gematria]], is used, such that א' = 1 = Sunday, and so forth. From this rule, every other date can be calculated by adding weeks and days until that date's possible day of the week can be derived.<ref>{{Cite web |last=Posner |first=Menachem |title=On Which Days Do Jewish Holidays Begin? |url=https://www.chabad.org/library/article_cdo/aid/5504248/jewish/On-Which-Days-Do-Jewish-Holidays-Begin.htm |website=Chabad.org}}</ref>