every 4 years.
http://wiki.answers.com/Q/How_much_time_between_ea...

1. Divide the year for which you are trying to determine a leap year by four. If the year is not divisible by four, it is not a leap year. If the year is divisible by four, continue
http://www.ehow.com/how_7546950_calculateleapyea...

1. Start off using the year you want to calculate. Ad. 2. See if it is. evenly. divisible by 4 (a whole number with no remainder) If it is not, like 1997, it is not a leap year. If
http://www.wikihow.com/CalculateLeapYears

Years that are divisible by 4, but not by 100, except when they're divisible by 400 are leap years. So the next one, as of this writing, is 2016. Update (29 February, 2012): The current
http://www.quora.com/Whenisthenextleapyear
