Okay, so the title is a bit misleading. Because for the most part, Leap Year is every four years.
But not all the time [insert dramatic soap-opera-esque turn to camera here].
Allow me to explain. I discovered this groundbreaking tidbit of knowledge just a few weeks ago, while conducting my late-night I-can't-sleep-so-I'll-just-surf-Wikipedia-for-useless-information ritual. I was concerned whether or not February had a Friday the 13th this year (lo and behold it did not, but better safe than sorry), so my surfing began there and slowly unlocked the secrets of our calendar.
As it turns out, we have been using the Gregorian calendar for well over 400 years (maybe most of you knew this. I, on the other hand, had no idea). The primary motivation for this new calendar was largely religious (something to do with Easter, I think. I'd research it for you if I cared), but it did correctly refine the length of a year by 0.002 percent relative to the previous Julian calendar. The refinement occurred because the calendar reduced the number of leap years within four centuries -- from 100 down to 97.
So what does this mean for Leap Day? As it turns out, our calendar skips Leap Day every centurial year (1700, 1800, 1900, etc). The skip means that, in some years, we actually go eight years without February 29th.
I know what you're thinking -- what about the year 2000? It wasn't that long ago and we definitely did not skip Leap Day.
Well according to the rules of the Gregorian calendar, the exceptions to this rule are centurial years evenly divisible by 400. On these years, we still keep Leap Day (complicated, I know). So far, this has happened only twice in the history of the Gregorian calendar: the year 1600 and the year 2000. Thus, we still had Leap Day in the year 2000.
Okay so why does this matter? Well if you happen to survive to the year 2100, remember this article and be prepared to skip Leap Year (okay, so maybe reading this article was a waste of your time).
But what about the Leap Day babies -- those rare souls born on February 29th?
This means that if you live to the year 2096 (you might be turning 25 or so) then buckle up: you'll need to hang in there for another 8 years if you want to see your next birthday.
That is, unless, you can convince the world to change the calendar yet again.