Daniel's timeline - Yom Kippur dates 2024 Hello,

I have been working on a hypothetical Daniel’s timeline for the final “week” of 7 years prophecy (using dispensational/literal interpretation of days in the timeline) described in Daniel/Revelation.  I am using the Hebrew feast days, holidays, and other possible prophetic events as guidelines for the spacing of literal days.  I was able to put together this figure for educational purposes. However, I found a discrepancy between the Yom Kippur feast day dates given at Hebcal.com vs. Torahcalendar.com in 2024.  The dates differ by one whole month – roughly YK Oct 12, 2024 vs. YK Sept 12, 2024.  I can’t find any real explanation about this discrepancy.  Hebcal.com seems to be correct with the Hebrew leap years.  The differences in how the sites make calculations does not seem to account for a whole month difference in dates.  Does anyone have an explanation for the date differences in this case?

P.S. Torahcalendar.com is not used by Jews for the most part.  I believe it is Messianic Christian in origin.  They don't give contact information.  I do not think this question asked from a Christian perspective would be appreciated on the Judaism stack exchange.

Thanks
The Biblical calendar is a "bound lunar" calendar. This means it consists of an exact number of lunar months, but the number of months in any particular year is 12 or 13. This ensures that Passover and other festivals  are always about the same time of year, but not exactly. This differs from the Islamic calendar,  which is "fixed lunar", in which a year is always 12 lunar months, and so Ramadan, and other Islamic observations drift earlier each year. 

The question then arises as to whether any particular year in calendars with a Biblical basis should be 12 months or 13. The governing principle is that the Passover, in the month of Nisan, must be after the vernal equinox. If 12 months after the last Passover takes us to a full moon prior to the vernal equinox,  then an extra month must be added before Nisan, and so Passover will be  thirteen months later, not twelve.

12 full moons after Passover 2023 brings us to 25th March 2024. Since this is after the vernal equinox there is no need to add a thirteenth month. Passover is, according to the Biblical principle, March 25th, and Yom Kippur is , as always,  a lttle under 6 months later. That is what Torahcalendar does,  by directly applying astronmical facts to Biblical principles.

Modern Jews, like Catholic,  Protestant and Orthodox Christians, use mathematical models of the sun and moon when calculating Passover/Easter.  In this method a thirteenth month is added on a regular basis 7 times every 19 years. However this has drifted somewhat. The result is that a thirteenth month is added before Nisan 2024. This makes Passover April 23rd 2024, with Yom Kippur a little under 6 months later, October 12.

The month discrepancy is accounted for by the fact that the Rabinic Calendar wrongly (from the astronomical perspective) adds a thirteenth month in 2024 although it is not required or needed to ensure Passover is in the Spring. This will also occur in 2043, 2062 etc.