How many days until First day of fall (autumnal equinox)?

Astronomical fall begins at the September equinox, the instant the Sun crosses the celestial equator heading south. That moment is set by the Earth's orbit rather than a calendar rule, so it drifts about six hours later each year and jumps back a day after every leap year. In 2026 it arrives at 00:05 UTC on September 23, which is 8:05 pm Eastern on September 22; in 2027 it moves to 06:01 UTC on September 23. The dates in the table are the US calendar dates published by the US Naval Observatory. Meteorologists use a simpler definition, with fall running September 1 to November 30, so a weather forecast may say autumn started three weeks before this countdown reaches zero.

What actually changes on the day: daylight and darkness are close to equal everywhere on Earth, and from here the northern United States loses roughly two to three minutes of daylight every day until the December solstice. The Harvest Moon is the full moon closest to the equinox, most US pumpkin patches and apple orchards open the weekend before, and it is the traditional cutoff for planting garlic and spring bulbs across the northern states. Clocks do not move yet: Daylight Saving Time ends on the first Sunday of November, about six weeks later, so sunsets get earlier gradually rather than all at once.

Korea and the rest of East Asia mark the same instant as Chubun, one of the 24 solar terms, though the traditional seasonal calendar there starts autumn at Ipchu in early August. In the southern hemisphere this equinox is the first day of spring. Because it lands so close to the end of the third quarter, the equinox is also a handy anchor for year-end planning: December 31 is exactly 100 days after September 22, in leap years and common years alike.