But the new decade doesn't start until 2011!!!!

[Lachrymose]

If there's no "Zero Year" then what do we consider the first 12 months of our lives? After those 12 months, we become a year older. I turn 35 on my 35th birthday, not my 36th. Are people still in their 30s when they turn 40? 2011 will be the end of the first year of the decade. The decade will end when the new one begins in 2020.

CH

Hmmm...good point.

1 B.C. would be (essentially, I know it's supposedly not accurate, but I'm just using this as a moment in time) one year before the birth of Christ.

Therefore A.D. 1 would be a year after the birth of Christ.

So, the birth of Christ to A.D. 1 should be the "zero year".

[crashhelmet]

I want to add one more thought to this, to appease the mathematical minds.

We count our years in the decimal system, or Base 10. Those numbers start at 0 and end with 9. There is no actual 10. Just as in Binary, or Base 2, the numbers start at 0 and end at 1. There is no actual 2. (The number 2 in Decimal is 10 in Binary).

CH

[Bright Star]

Something that occured to me: For example-the 1980's is said to have started in 1980. BUT isn't it also a part of the 70's as well? Any year ending in zero could be the start of one decade & at the same time the beginning of another. sort of like a "gateway year".
So 2010 would be the beginning of the 2nd decade of the 21st century AND also the the end of the first decade of the 21st century.
That's another way of looking at it.