What you want is called "astronomical year numbering" (https://en.wikipedia.org/wiki/Astronomical_year_numbering https://en.wikipedia.org/wiki/Astronomical_year

What you want is called "astronomical year numbering" (https://en.wikipedia.org/wiki/Astronomical_year_numbering https://en.wikipedia.org/wiki/Astronomical_year_numbering), so you have 1 BC = 0, 2 BC = -1, and so on. Astronomers are about the only people who would need to do math on negative years.