Final answer:
The elected president officially becomes President of the United States on January 20th, known as Inauguration Day.
Step-by-step explanation:
The elected president officially becomes President of the United States on January 20th following the election. This date is known as Inauguration Day. It is when the president takes the oath of office and delivers an inaugural address, marking the beginning of their term in office. The first Inauguration Day took place on March 4, 1789, but it was later changed to January 20th with the passage of the 20th Amendment in 1933.
Learn more about Inauguration Day