There have been about 514 Leap Years since Caesar created it in 45BC. Without the extra day every 4 years, today would be July 28, 2013. Also, the Mayan calendar did not account for leap year…so technically the world should have ended 7 months ago
The above quote, while true in a strict technical sense (indeed Mayans did not have leap years as we understand them), demonstrates a fundamental misunderstanding of how the Mayans kept track of time.
Currently, we use a calendar called the Gregorian Calendar which is based upon the solar cycle, which is 365.2425 days long. Since a solar year is longer than a calendar year by a few hours, we have to compensate for that difference or the seasons start to drift out of alignment with the dates and we end up with snow in July. The Gregorian Calendar does this by adding an extra day every four years. The years in which this happen are called leap years. Unfortunately, those extra few hours at the end of each solar year don't quite add up to a quarter of a day, so, in order to further compensate for this discrepancy, the Gregorian Calendar ignores the leap year rule in years that are evenly divisible by 100, unless those years are also evenly divisible by 400. So, for example, the years 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not.
The Mayans viewed time in a completely different manner than we do today. They used a system of calendars based upon different methods structured around several cycles or "counts" of varying length to keep track of time. They had a 260 day calendar called the Tzolk'in which combined a system of 20 days with 13 numbers. The also used at 365 day calendar (360 named days plus 5 unnamed days at the end of the year) called the Haab' which was the foundation of their agrarian calendar and used month names that were based on the seasons and agricultural events. Mayans used both the Tzolk'in and the Haab' when recording dates to form a synchronized cycle lasting for 52 Haabs. The passage of 52 Haabs was referred to as a "calendar round". After the passage of 1508 Haabs (29 calendar rounds), 365 extra days would have had to have been adjusted for and it just so happens that the solar cycle and Haab count reset to zero after 1508 tropical years. This means that the Haab calendar auto-adjusted for leap years, it just took 1508 years to do so.
In order to keep track of time over periods longer than 52 years, Mayans utilized the Long Count calendar which is what this whole Mayan Doomsday hoopla is based upon. The Long Count keeps track of days by using a base-20 and base-18 scheme rather than the base-10 scheme that we usually use. The calendar was broken up into sections. A k'in was equal to a day. After 20 days, the k'in number would reset to zero. A winal equaled 20 k'in and would reset to zero after 18 winals had passed. A tun equaled 18 winals and would reset to zero after 20 tuns had passed. A k'atun equaled 20 tuns and would reset to zero after 20 k'atuns would pass. A b'ak'tun equaled 20 k'atuns. A b'ak'tun is roughly equal to 394.3 solar years.
Using the Long Count calendar, today's date (March 7, 2012) would roughly be expressed as: 220.127.116.11.11 (12 b'ak'tun, 19 k'atun, 19 tun, 19 winal, 11 k'in). Doomsday alarmists are all in a panic because sometime on December 21, 2012, the Mayan Calendar is going to hit 13 b'ak'tun or 18.104.22.168.0 and that sort of resetting of the numbers is seen as a significant event. The calendar isn't ending, it's just adding 1 more to the number of b'ak'tuns and resetting all the other numbers to zero. The same sort of thing happened on September 18, 1618 when the Long Count date reached 22.214.171.124.0 and on June 15, 1224 when the Long Count date reached 126.96.36.199.0 and so forth. And the world is still here.
When I first saw the leap year quote on Facebook, I typed out a long response debunking it. When I saw it again, I typed out a shorter response. Soon, I trimmed down my responses to something like "The Mayans were aware of it and corrected for it. The people who compared our current calendar to the Mayan Calendar were also aware of the differences and compensated for it". Now, after seeing the quote so many times over the past week, I find that I'm tired of trying to educate people on it. And it's a waste of time because the quote incorrectly debunks something that didn't need to be debunked in the first place. Anyone who's actually stupid enough to believe in Mayan Calendar doomsday prophecies is already far out of the logical loop anyways. It's on a par with believing that the world will end on December 31, 2012 because the calendar that I bought at Wal-Mart ends on that day. So, if people want to post that stupid quote and feel like they're smarter than these crazy doomsday predictors, it's still a net gain.