How Long Does it Take to Earn a PhD in Economics?
Ideally, you should be able to finish in four years. During the first two years you will complete the core courses. Generally after the first or second year you will take comprehensive exams to show that you have learned and retained basic skills. In the third and fourth year you will complete your coursework by taking field courses and at least get a solid start on your thesis.
However, only 55% of students who start in Economics PhD programs eventually earn their degree. The median time to graduation is 5.3 years and the mean is over 6. My casual observations suggest that If you are less prepared, enroll in a program that challenges you, get a job before you complete your thesis, change your mind about you thesis and start working on a different topic, and so forth, it can easily take you six years or longer -- though some of those six years might have been spent working on a thesis while holding a job.
The statistics reported above came mostly from "So You Want to Earn a PhD in Economics? How Long do You Think it Will Take?" by John Siegfried and Wendy Stock from the Journal of Human Resources in Spring 2001 pages 364-78. They also find that students who already have master's degrees tend to graduate about 7 months faster and that women with children tend to take about 10 months longer. Otherwise gender, size of program, age, marital status, and race don't appear clearly associated with the time it takes to complete a degree.