Autumn starts on different dates depending on the definition used:
- According to the meteorological calendar , autumn always starts on September 1 and ends on November 30. This calendar divides the year into four fixed three-month periods for consistency in weather statistics.
- According to the astronomical calendar , autumn begins with the autumnal equinox , which occurs around September 22 or 23 each year, and ends with the winter solstice around December 21 or 22. In 2025, astronomical autumn starts on Monday, September 22.
Thus, if using the common meteorological definition, autumn starts September 1, but astronomically, it starts with the equinox around September 22. These two definitions are widely accepted and used for different purposes such as weather forecasting and astronomy.
