How Many Days Until the Autumn Equinox?

the Autumn Equinox 2026 is Wednesday, 23 September 2026

There are 35 days between 19 August 2026 and the Autumn Equinox, which falls on Wednesday, 23 September 2026. That is exactly 5 weeks, or 24 working days once Saturdays, Sundays and the US federal holidays in between are taken out — the figure that matters if you are counting delivery lead time or a work schedule rather than sleeps. The date is 2026-09-23 in ISO form and 9/23/2026 in the US format, it falls in ISO week 39 of 2026, and it is day 266 of 365.

How the date of the Autumn Equinox is decided

The September equinox, falling on 22 or 23 September.

That makes it a computed date: there is no fixed day and no simple weekday rule, so it has to be worked out from a formula or a calendar of its own each year. In 2026 it works out as Wednesday 23 September.

the Autumn Equinox is an observance rather than a federal holiday. Offices, banks and schools stay open unless an individual employer chooses otherwise, and it counts as an ordinary business day in every calculator here. Only the eleven federal holidays are treated as non-working days — the list and the reasoning are on the holiday sources page.

the Autumn Equinox in the years after 2026

Both the date and the weekday move, because the rule is not tied to either.

Every convention used above — whether the start date counts, how month ends are clamped, which holidays close an office — is written out on the methodology page, including how we count the 24 working days above.