Is There Any Reason the Last Digit of the Jewish Year and Last Digit of the Civil Year Are the Same?

I’ve often wondered, without taking the trouble to look into it, whether there is any particular reason that the last digit of the Jewish year and last digit of the once Christian and now universal civil year are the same. Or rather, they’re the same for eight or nine months of the twelve, from January 1 until Rosh Hashanah. From now until next September 6, we will be living in 5781 and 2021. Then, when the Jewish new year sets in, we will be in 5782 and 2021 until January 1 comes around again and 2021 becomes 2022.

Is this sameness of last digits a coincidence? Why, after all, should there be any connection between the Jewish system of chronology, whose Year One is the year of Creation, and the Christian system, whose Year One is the year of the birth of Jesus?

Before jumping to any conclusions, however, two things need to be pointed out. The first is that neither the Christian nor the Jewish systems were the ones originally used by Christians and Jews when they began to date the years in terms of a single starting point. The second is that the system we today call “Jewish” was in use in much of Christendom well before it was adopted by Judaism.