The first year in the actual calendar (also called Gregorian, or modern calendar) was 1582, when it was instituted by Pope Gregory XIII. Before of this, another calendar, the Julian, was in use, with slightly different rules. The actual modern calendar though will get out of sync by 1 day with the astronomical calendar around the year of 4818 (after ≈ 3236 of years from its creation in 1582).
Count them if you wish, in the list below.