List of presidents of the United States by time in office

The length of a full four-year term of office for a president of the United States usually amounts to 1,461 days (three common years of 365 days plus one leap year of 366 days). The listed number of days is calculated as the difference between dates, which counts the number of calendar days except the first day (day zero). If the first day were included, all numbers would be one day more, except Grover Cleveland would have two more days, as he served two full nonconsecutive terms.

Of the individuals elected president, four died of natural causes while in office (William Henry Harrison, Zachary Taylor, Warren G. Harding, and Franklin D. Roosevelt), four were assassinated (Abraham Lincoln, James A. Garfield, William McKinley, and John F. Kennedy), and one resigned from office (Richard Nixon).

William Henry Harrison spent the shortest time in office, while Franklin D. Roosevelt spent the longest. Roosevelt is the only American president to have served more than two terms. Following ratification of the Twenty-second Amendment in 1951, presidents—beginning with Dwight D. Eisenhower—have been ineligible for election to a third term or, after serving more than two years of a term to which some other person was elected president, to a second term. The amendment contained a grandfather clause that explicitly exempted the incumbent president, then Harry S. Truman, from the new term limitation.