Inquiring minds want to know.....

https://www.usconstitution.net/consttop_term.html

In the beginning...

The first President, George Washington, was sworn into office on April 30, 1789. He had been chosen by the Electoral College, by what most people felt was a foregone conclusion, the February before. Why April 30th? The date is certainly not spelled out in the original Constitution. The date was set more by circumstance than anything else.

When New Hampshire ratified the Constitution, word was sent to the Confederation Congress, which then decided, in effect, to dissolve itself. It set the dates for the next series of events to take place under the new Constitution: On January 7, 1789, states would choose electors. On February 4, 1789, the electors would cast their ballots for President. On March 4, 1789, the new legislature would meet to begin business.

Mostly because of poor weather, it was not until April 6, 1789 that a quorum of Congress arrived in New York City to count the electoral votes. Once the counting was done, word of Washington's election was transmitted to him. He received the notice on April 14 and replied that same day, accepting his election. After making ready, Washington left his home at Mount Vernon on April 16. He arrived in New York on the 23rd and basically cooled his heels while the House and Senate worked out the details of the inauguration. The 30th was the date arrived at during those negotiations.

During Washington's first term, the Congress passed a law setting March 4 as the date for future inaugurations. When Washington took his second oath of office, then, it was on March 4, 1793. His first term was almost two months shy of a full four years. Subsequent inaugurations were held on March 4 as a matter of law, until the second inauguration of Thomas Jefferson on March 4, 1805.