Many Christians believe that a 360-day calendar is required for interpreting prophecy. Where did this belief come from? And is it essential for interpreting prophecy?

Judaism did not have a 360-day calendar that was used for everyday use¹ and definitely not for any religious use², and there is no evidence in Scripture that any prophecy relies on a 360-day calendar. There is great detail available online to see how time is calculated in Judaism. A simple explanation can be found here:

Some apparently equate where the woman flees for 1260 days in Revelation 11, 12 and 13, to the 42 months mentioned in Revelation 13, making each month 30 days. But the Bible does not expressly equate these two separate time periods relating to two separate events. And evidence shows that the Jews did not use a 360 day calendar in any real sense, they even added an intercalary month 7 times every 19 years, in an effort to align their calendars. Over time however, Jews refined their calendars to ensure they kept the feasts at their appointed times.

While not in the protestant Bible, the Book of Enoch (72:8-32) states:

On that day the night decreases and amounts to nine parts, and the day to nine parts, and the night is equal to the day and the year is exactly as to its days three hundred and sixty-four.

The book explains that there are 30 days for 8 months and 31 for 4 months. This averages at 30.333 days/month. To put it another way,

The Book Of Jubilees (6:32):

And command thou the children of Israel that they observe the years according to this reckoning-three hundred and sixty-four days, and (these) will constitute a complete year, and they will not disturb its time from its days and from its feasts; for everything will fall out in them according to their testimony, and they will not leave out any day nor disturb any feasts.

Once the Jews were exiled to Babylon (Daniel’s time) they refined their calendar and it is practically indistinguishable from our solar calendar today. Moreover, when God gave the “70 sevens” prophecy to Daniel (Jews called a week of days a “seven”), so 490 years, the solar calendar was used, not a 360-day calendar. Looking at the 483 years before ministry of the Messiah, circa AD 30 (see post explaining why this is the start, not end of the ministry), puts the command to rebuild Jerusalem (Dan 9:25), the command by Artaxerxes I, circa BC 457 ³. There is no conversion to 360-day years for this to be. It also sets the precedent that 1 day = 1 solar year. Ezekiel 4 also explicitly used this principle.

However there is another possible explanation to account for the apparent misalignment of 42 months and 1260 days of Revelation 11.

They are similar, but not identical periods of time.

Let’s assume they are solar years, 365.24219 days of average duration. 42 months is 1278 days, meaning that the length the city is trampled is 1278 years, and the time of the two witnesses is 1260 years (Revelation 11) and the time of the Sea Beast is 1278 years, and the time Israel flees is 1260 years (Revelation 13 & 12). Read the pages on those for more detail.

Does this matter? Yes.

There are 18 years between the start of construction of the Dome of the Rock (AD 688), and Jews being expelled from the temple mount at the completion of the Al Aqsa mosque (AD 705). It is also the time difference between Israel regaining the control of the Temple Mount (AD. 1967) and Israel regaining control of Israel (AD. 1949).

In short, it’s an unnecessary distraction, arguing about 360-day calendars, when Scripture does not demand it and there is no solid evidence to suggest this is the required way to interpret the prophecies of Daniel 7, 9 & 12, and Revelation 11, 12 & 13. In fact, the solar year is used in fulfillment of Daniel’s 70 week prophecy. In my view, the juxtaposition of 1260 with 42 months, actually explains some time discrepancies we see in historical events, lending credence to the idea that a solar calendar is the preferred method, and that the 360-day “prophetic” calendar is an unbliblical invention.

FOOTNOTES:

1. Administrators in ancient Judah used schematic 30-day months and a 360-day year alongside other annual frameworks. This year was never practiced as a “calendar” for any cultic or administrative purpose, but rather served as a convenient framework for long-term planning, as well as for literary accounts that were not anchored to a concrete calendar year. [https://www.cambridge.org/core/journals/harvard-theological-review/article/360day-administrative-year-in-ancient-israel-judahite-portable-calendars-and-the-flood-account/8F5696178CD94A096EA16DC811FC787D]
2. Israel was commanded to keep the festivals on particular days. To quote Bochum. “At least, most OT scholars today acknowledge, that early Judaism was bitterly divided on the issue of the calendar. The reason for such strife should be obvious: if one adheres to a defective cultic calendar one will inadvertently end up celebrating the great religious festivals on days when Yahweh did not command them to be held, which would be tantamount to blasphemy. Moreover, if one’s calendar was out of step with the calendar presupposed by the divine ordinances, one would equally unfortunately come to trespass against the sabbath restrictions.” Bochum goes on to describe the use of a 364-day calendar. https://www.tandfonline.com/doi/abs/10.1080/09018328708584870?journalCode=sold20
3. https://biblearchaeology.org/abr-projects-main/the-daniel-9-24-27-project-2/4589-the-going-forth-of-artaxerxes-decree-part1
   https://www.perspectivedigest.org/archive/27-4/the-decree-to-restore-and-build-jerusalem1