This is a list of U.S. Chief Justices by time in office. This is based on the difference between dates; if counted by number of calendar days all the figures would be one greater.
§ Historians disagree as to whether William Cushing resigned (and, therefore, held the position) or declined the commission (and never held the position at all)
Trivia
In order to surpass the tenure of his immediate predecessor William Rehnquist, John Roberts will have to serve as Chief Justice until Saturday, September 7, 2024. Roberts will be 69 years old on that date.
In order to surpass John Marshall as the longest-serving Chief Justice in history, John Roberts will have to serve as Chief Justice until Wednesday, March 1, 2040. Roberts will be 85 years old on that date.
In order to surpass William O. Douglas as the longest serving Supreme Court Justice in history, John Roberts will have to serve on the Supreme Court until Saturday, April 26, 2042. Roberts will be 87 years old on that date.