How many days are in autumn?

Autumn is three months long, from the autumnal equinox to the winter solstice. This will be from mid-September to mid-December in the Northern Hemisphere and mid-March to mid-June in the Southern Hemisphere. In terms of days, autumn can be considered to last either 91 or 92 days (one fourth of the year).

In the Northern Hemisphere, autumn (fall) begins on September 22 or 23 and ends on December 21 or 22.
In the Southern Hemisphere, autumn begins on March 20 or March 21 and ends on June 20 or June 21.