Pirates of the Caribbean: The Curse of the Black Pearl (2003)
Pirates of the Caribbean: Dead Man's Chest (2006)
Pirates of the Caribbean: At World's End (2007)
Pirates of the Caribbean: On Stranger Tides (2011)
Planned: Pirates of the Caribbean: Dead Men Tell No Tales (2017)
So 3 years, 1 year and 4 years. And potentially now 6 years.
This is from the Pirates Wiki...
A timeline of events as depicted and mentioned in the Pirates of the Caribbean franchise. A specific date for the placement of the first three films has not been given. Though the film's scriptwriters, while making the first film, placed them in a "floating thirty-year environment" set in the 18th century, sometime around the 1720s to 1750s. Although On Stranger Tides was said to be placed at the year 1750.
...this gets more in depth. Guess it takes stories/events outside the movies and ties things together.
http://pirates.wikia.com/wiki/Timeline_of_Pirates_of_the_Caribbean_series