Year of Creation

1st of Tishrei, Hebrew Year 1 = Mon, 7 September 3760 B.C.E.

https://www.hebcal.com/converter?hd=1&hm=Tishrei&hy=1&h2g=1

To find the corresponding Jewish year for any year on the Gregorian calendar, add 3760 to the Gregorian number, if it is before Rosh Hashanah. After Rosh Hashanah, add 3761.

The question is which Hebrew year is year 1.
As far as I know, and as also written in Wikipedia here, when we count from the creation of the world (beriat haolam), the world was created on 25 Elul year 1 and the first Rosh Hashana on 1 Tishri was year 2.

There was no 1 Tishri 1.

Is this a bug in Hebcal or you do not count from the creation of the world?

Daniel, thanks for this. I really appreciated the background reading, so thanks for sharing those sources! I realize I misunderstood your initial question.

To answer your question about calculations, Hebcal doesn't count forward from the creation of the world. Rather, it calculates dates using a set of mathematical formulas. The dates all are relative to an "epoch", which is an arbitrary point in time. In our case, the epoch is set to the arbitrary/imaginary date 1 Tishrei 1. Once the epoch is fixed, all further calculations are done relative to the epoch.

In any case, your original question asked: Why does HebCal return -3759?

If that's still an important thread, could you send a screenshot or a URL of some place where Hebcal is displaying -3759 with respect to Hebrew Year 1? 

When I convert 1 Tishri 1 to Gregorian, I get Mon, 7 September 3760 B.C.E.
Whether this is correct or not depends on how you count years.
If you count from Adam then it should be a Friday.

If you count from Creation then 1 Tishri of year 2 should be a Friday but the converter returns Sat, 28 August 3759 B.C.E..

If we look at years:

- year 5783 starts in 2022

- year 3762 starts in year 1 (5783 - 2021)

- year 3761 starts in year -1 (there was no 0)

- year 1 starts in -3761 (-1 - 3760)

We can look at it from the Gregorian side:

- year 2022 has rosh hashana of 5783

- year 1 has rosh hashana of 5783 - 2021 = 3762

- year -1 has rosh hashana of 3762 - 1 = 3761

- to know when was rosh hashana of year 1: -1 - 3760 = -3761 

or just run this python:

g = 2022
for h in reversed(range(1, 5784)):
    if g in [-1, 0, 1, 2022] or h == 1:
        print(f"{g} - {h}")
    g = g - 1
    if g == 0: g = -1

Therefore I think Hebcal is a bug

Minor edit to above post: the routines that would require work to account for the Gregorian reformation are actually the Gregorian routines, not the Hebrew date routines.

Golang: FromRD, ToRD

https://github.com/hebcal/greg/blob/main/greg.go

ECMAScript: greg2abs, abs2greg, toFixed, yearFromFixed, etc.

https://github.com/hebcal/hebcal-es6/blob/main/src/greg0.js

Michael, I will work on fixing the dates. I'll probably reach out separately to understand how to run the code locally for testing.

But what about the years? 1 Tishri 1 should start in Gregorian -3761