Which day is the first day of the 21st century... ?

Question

is it Jan. 1 2000 or jan. 1 2001 and why?

Answer 1

Kicking is exactly right and for the right reason.  

Answer 2

1/1/01 beacuse there was no year 0....100 complete years goes through year 100 on through 2000.  Hope this doesn't oversimplify and makes sense.

Answer 3

Jan. 1, 2001

Each century is a block of 100 years. The first century began with the year 1 and continued through the end of year 100. The second century was the years 101-200, and so on.

There was no year 0 in our standard numbering (the A.D. or CE dating system). The year before our year 1 was 1 B.C. (or BCE), which was the end of the first century B.C. (or BCE).

[If you're not familiar with them, CE (Common Era) and BCE (Before CE) are religion-neutral equivalents of A.D. and B.C.]