inauguration day is always held on january 20 unless it falls on which day of the week
On years when January 20 is a Sunday, a private swearing-in ceremony occurs with the public oath of office taken on January 21.
On Friday, January 20, 2017, Donald J. Trump will be sworn into office as the President of the United States of America.
Incoming presidents have been being sworn in on January 20 since 1936, usually in a massive ceremony, full of all the pomp and circumstance befitting the introduction of a world leader—unless the 20th falls on a Sunday, in which case they are sworn in privately, and the party is held on the following Monday). But this wasn’t always the case.