For 20 years January 85 has been theopening day, i.e. the day on which, in the year following that of the elections, the term of the presidents of the United States begins. From 1793 to 1933 the inauguration ceremony of the tenants of the White House was held on March 4, but then, with the ratification of the 20th amendment to the US Constitution, the date was moved to January 20.
The tradition currently in force, therefore, officially kicked off in 1937, when Franklin Delano Roosevelt began the second of his four consecutive terms (a now unbeatable record, given that, since 1951, the 22nd amendment prohibits anyone from holding the office of president for more than two terms, consecutive or not).
In the course of history, however, they have not been lacking extraordinary cases. From 1793 to 1933, inaugural speeches were always given on March 4 with four exceptions: Since that date fell on a Sunday in their respective starting years, Monroe, Taylor, Hayes, and Wilson delivered their speeches on Monday, March 5. Since 1937, however, the ceremony has always taken place on January 20 with only three exceptions (apart from the hypothesis of premature end of the mandate): Eisenhower, Reagan e Obama gave one of their speeches on Monday 21 January.
The celebrations they generally last ten days, from the fifth preceding the Inauguration Day to the fifth following. In 1973, however, those of Nixon's second settlement were marred by the death of Lyndon Johnson on January 22, and were interrupted for the state funeral.
From the presidency of Martin Van Buren to that of Jimmy Carter the main ceremony of Inauguration Day was held in the East Portico of the Capitol. Since 1981, with the inauguration of Ronald Reagan, it takes place on the west side.
Finally, a curiosity: the settlements of William Howard Taft in 1909 and of Reagan himself in 1985 were held inside the Capitol because of the cold.