If we are in the 21st century, why do our years start with 20?

  

2000
2001
2002
  Our "century" will always be one higher than our calendar year because years 1-99 were never considered to be the start of the'first' century - the first century 'started' when the year 99 ended.  The first century started at the year 100, not 1.   It can be a bit confusing. So, in keeping with that, the year 1999 ended the 20th century and the 21st century began at the year 2000. 

  

 Trivia Challenge #3