How Many Days Until the Autumn Equinox 2027?

the Autumn Equinox 2027 is Thursday, 23 September 2027

There are 400 days between 19 August 2026 and the Autumn Equinox 2027, which falls on Thursday, 23 September 2027. That is 57 weeks and 1 day, or 274 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 2027-09-23 in ISO form and 9/23/2027 in the US format, it falls in ISO week 38 of 2027, 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 2027 it works out as Thursday 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 2027

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 274 working days above.