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The Millennium

The second millennium and the twentieth century both end at midnight on December 31, 2000.  They did not end at the end of 1999. 

This has become a big pet peeve of mine.  I have heard even sources that I would expect to know better, like the New York Times, National Public Radio, and President Clinton1 incorrectly state that the new millennium begins with the year 2000.  I decided to post this page in the hope that it will help at least some people stop incorrectly identifying the end of the millennium.

By the way, I have no problem with people who wanted to throw a big party at the end of 1999.  We even considered having one (but ended up just going to one).2  After all, who could argue with an excuse for another party?  But these parties should not have been called "Millennium Parties" or "21st Century Parties".  Instead, they should have been called "Parties to Celebrate the End of Years That Start With '1' and the Beginning of Years That Start With '2'".3

Also, I'm not going to get into the issue of whether the appropriate measurement of dates is a calendar based on Christian mythology.  And for the sake of ease and clarity, I have used the traditional notations of BC for years before year 1 and AD for year 1 and later, rather than the more culturally neutral notations of CE (Common Era) and BCE (Before Common Era), which some readers might not recognize.

Let me begin my diatribe with a few references to authority.  From the U.S. Naval Observatory, Time Service Department ("The Official Source of Time Used in the United States") - -

"The end of the second millennium and the beginning of the third will be reached on January 1, 2001. This date is based on a now globally recognized calendar established by the sixth-century scholar Dionysius Exiguus, who was compiling a table of dates of Easter. Rather than starting with the year zero, years in this calendar begin with the date January 1, 1 Anno Domini (AD). Consequently, the next millennium does not begin until January 1, 2001AD."

This information is repeated on the White House web page at  

But in case you think this is some government conspiracy of misinformation, allow me to explain why the third millennium begins on 1/1/2001.

Think of the years displayed linearly, as on a ruler.  On a ruler, everything up to the 1 inch mark is referred to as the first inch (or "inch 1").  A foot has 12 inches. The first foot of a measuring tape ends at the end of the inch 12. 

With years, the first year ended at the end of "year 1".  The second year ended at the end of year 2.  And so on.

A century has 100 years.  The first century ended at the end of year 100.  The 20th century ends at the end of the year 2000 (December 31, 2000).  The 21st century begins at the beginning of the 2001st year (January 1, 2001).

A millennium has 1000 years. The first millennium ended at the end of the 1000th year.  The second millennium ends and the end end of the year 2000   (December 31, 2000).  The third millennium begins at the beginning of the 2001st year (January 1, 2001).

One might argue that this is the case only because a mistake was made in not having a "year 0" and therefore our calendar is actually off by one year.  This argument fails because the decision to not have a "year 0" was mathematically correct - just like there is mathematically no "inch 0".  To continue with the ruler comparison, the transition from BC to AD is the same as the transition from a negative distance to a positive distance. Consider point X as the beginning of a ruler or measuring tape. 12 inches to the right of point X is point A.  The 12 inches between points X and A can be thought of as inch 1, inch 2, inch 3, etc., up to inch 12. And again, inch 1 is the distance from the beginning of the ruler (point X) up to the point marked as 1 inch. 12 inches to the left of point x is point B. The 12 inches between points X and B can be thought of as inch -1, inch -2, etc., up to inch -12. And inch -1 is the distance from point X to the end of the first negative inch. So now, from point A to point B we have 24 inches ranging from "inch -12" to "inch 12".   Notice that there is no "inch 0". The inches have to be counted this way in order for simple mathematical calculations to make sense. To determine the distance between two points on our imaginary ruler, you simply subtract one number from the other. How far is it from the end of inch 12 to the end of inch 8?  It is 4 inches (12 - 8 = 4).  How far is it from the end of inch 8 to the end of inch -4? 12 inches (8 - (-4) = 12). If there were an extra inch ("inch 0") thrown in there between inch 1 and inch -1, all these calculations would be thrown off.

Similarly with years. How long was it from 10 BC to 10 AD? 20 years (10 - (-10) = 20). If there were a "year 0" in between "year -1" and "year 1", these calculations wouldn't work. The transition point from BC to AD is like the point X in the ruler example. Point X has no length itself. The inch after point X is "inch 1". The inch before point X is "inch -1".  There is no room left for an "inch 0". Similarly, the year after the transition from BC to AD is year 1 AD, the year before that point is year 1 BC (which could also be though of as "year -1"). There is no room for a "year 0".4 

Here are some other sites that explain this:


1.  In his otherwise admirable 1999 State of the Union Address, delivered January 19, 1999, President Bill Clinton stated, "barely more than 300 days from now, we will cross that bridge into the new millennium."  (see   That was a little more than 300 days from the year 2000, but it was more like 700 days until the new millennium.

2.  In fact, about 16 years ago I promised a bunch of people in my high school that I would have a huge party at the end of 1999 -- and some people still remembered that and tried to hold me to that promise. 

3.  Perhaps the best reason to celebrate the end of 1999 is that we will not have to listen to the song "1999" by Prince anymore.

4.  If you were to insist on there being a "year 0",  I wonder on which side of the transition point you would place it? Or would you create two additional years - a year 0 BC and a year 0 AD?

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Last Updated 22 July 2005
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