The first day of fall in 2023 is on Saturday, September 23, 2023, at 2:50 a.m. EDT in the Northern Hemisphere. This is also known as the autumnal equinox, which is the day of the year when day and night are approximately equal in length all over the world. The date varies slightly year to year, but it is usually September 22 or 23, and on rare occasions, it can fall on September 21 or 24. If you live south of the equator, this is when spring will begin.