Anno Domini dating was first calculated in 525 and began to be adopted in Western Europe during the eighth century. The numbering of years per the Christian era is currently dominant in many places around the world, in both commercial and scientific use.

How did the year 1 start?

When Julius Caesar introduced his calendar in 45 B.C.E., he made 1 January the start of the year, and it was always the date on which the Solar Number and the Golden Number were incremented. Since about 1600 most countries have used 1 January as the first day of the year.