How Many Days Until Autumn?

This countdown tracks the Northern Hemisphere autumnal equinox. In the Southern Hemisphere, this exact same astronomical moment marks the start of Spring, not Autumn, since the two hemispheres experience opposite seasons at the same time of year.

The autumnal equinox is the moment the sun crosses directly over the equator heading south, the only two days of the year, along with the spring equinox, when day and night are close to equal length nearly everywhere on Earth. From this point forward, the Northern Hemisphere tilts increasingly away from the sun, days keep getting shorter, until the Winter Solstice in December.

A calendar year runs 365 days, but Earth's actual orbit takes about 365.24 days. That extra quarter day means the equinox lands roughly six hours later each year until a leap year adds a day back and resets it earlier. That's why Autumn typically starts somewhere between September 22 and 23 rather than on a perfectly fixed date, unlike a holiday such as Christmas that never moves.

This page uses the astronomical definition, tied to the equinox. Meteorologists use a simpler, fixed definition instead, meteorological Autumn always runs September 1 through November 30, based on the twelve month calendar rather than Earth's orbital position, which makes it easier to compare consistent three month blocks year over year for climate and weather record keeping.