I don't like the tone of the article but I couldn't find a better link:
Ok, I've been hearing this doomsday stuff about the Mayan calendar and it's prediction of the end of the world. Well, sometimes we just don't think of the obvious. Here is a little tidbit that may just relieve your mind a little.
The Earth orbits the sun every 365 and a quarter days. The calendar gains a day every four years.
In 45bc Caesar created the leap year so the ancient roman calendar would automatically correct itself as it does to this day.
The Mayan calendar did not take leap year into account so they were off buy several months.
Today, without these added extra days, would be around the beginning of August 2013.
The end of the world would have occurred in June of last year.
So take a breath, pay your taxes, maintain your 401K, open your Christmas savings account, and don't burn any bridges.
We can all have a good laugh at the foolish that went underground on December the 20th as they come sheepishly crawling out a few days later.
http://garyfcox.blogspot.com/2012/03/leap-year-and-mayan-calender.html
Basically, it talks about how the Mayan calendar didn't take into account leap years and thus, Dec. 21, 2012 would have already happened.