AnswerIt can vary a lot. A PhD program requires completing a serious project of original research. But as a guess, three to five years beyond a master's degree is pretty typical.
The doctorate would take approximately four years post bachelor's to complete. The degree can run up to 60 credits in coursework particular to a specific field of study. The actual length of time depends much on how long it takes a student to prepare and defend their dissertation which typically follows the prescribed coursework. The dissertation is an individual student project advancing an original view point on a topic of the students choosing. It is developed through extensive supporting research and must be approved by the designated committee.