To elaborate
Christmas …. a good time to think about it. If 1BC was the year before Bethlehem, and Jesus turned 1 at the end of the first year after Bethlehem (like all of us), was that the year 0 or 1 AD ?
It seems the US Naval Observatory, the Farmer’s Almanac, Dionysius and The Venerable Bede all say that under the Gregorian Calendar (which almost the whole world follows, still) and previous Julian system, the year before Bethlehem was 1 BC, BUT there was no year 0. Therefore the first decade began with the year 1 and the end of the tenth year was end of year 10.
Happy New year from he who is at present waiting for lunch on 2nd January 2020.
I would prefer to think of 2020 as the first year of the decade. I never have liked it that one minute after 11:59 AM is 12:00 PM. To me noon makes more sense as 12:00 AM and midnight as 12:00 PM.