Fall in the Northern Hemisphere starts with the autumnal equinox, which in 2025 will occur on Monday, September 22. This marks the official first day of fall, when day and night are roughly equal in length. Fall will last until the winter solstice around December 21, 2025. In the Southern Hemisphere, fall begins with the March equinox, so the timing is opposite to the Northern Hemisphere. There are two main ways to define the start of fall:

• Astronomical fall begins at the moment of the autumnal equinox (September 22 or 23 usually).
• Meteorological fall starts on September 1 and ends on November 30 for practical seasonal grouping.

For 2025:

• Astronomical fall starts on September 22 at about 2:19 PM EDT in the U.S.
• Meteorological fall starts on September 1.

So, the widely accepted official start of fall is September 22, 2025, for the Northern Hemisphere, lasting until December 21, 2025.