First Day of Autumn

First Day of Autumn 2025: When Does Fall Start?

The first day of autumn, also known as the autumnal equinox or fall equinox, marks the astronomical beginning of the fall season. In 2025, the autumn equinox in the Northern Hemisphere falls on September 22, while the Southern Hemisphere experiences its autumn equinox in March. Use our calculator above to find the exact date and time for any year between 2000 and 2040.

What Is the Autumn Equinox?

The autumn equinox is an astronomical event that occurs when the Sun crosses the celestial equator moving from north to south (in the Northern Hemisphere) or from south to north (in the Southern Hemisphere). On the equinox, day and night are nearly equal in length — the word "equinox" comes from Latin aequus (equal) and nox (night). This event signals the transition from summer to autumn and brings shorter days, cooler temperatures, and changing foliage.

Astronomical vs Meteorological Autumn

There are two ways to define the start of autumn. Astronomical autumn is based on the Earth's position relative to the Sun and begins on the date of the autumn equinox, which varies between September 21–24 in the Northern Hemisphere and March 19–22 in the Southern Hemisphere. Meteorological autumn follows a fixed calendar and always starts on September 1 in the Northern Hemisphere and March 1 in the Southern Hemisphere, making it easier for weather record-keeping and climate comparisons.

When Is the Autumn Equinox?

In the Northern Hemisphere, the autumn equinox occurs around September 22 or 23 each year. In the Southern Hemisphere, the autumn equinox occurs around March 20 or 21. The exact timing depends on the Earth's orbital position and can shift slightly due to leap years and other gravitational factors. Use our interactive tool above to see the precise UTC date and time for any year from 2000 to 2040.

Why Does the Date of the Equinox Change?

The date of the equinox varies because the Earth's orbit around the Sun takes approximately 365.25 days, while our calendar year is 365 days (with leap years adding an extra day every four years). This mismatch causes the equinox to shift by about 6 hours each year, with leap years resetting the cycle. Additionally, gravitational perturbations from other planets slightly affect Earth's orbit, introducing minor variations in equinox timing.

Traditions and Celebrations Around the Autumn Equinox

Many cultures celebrate the autumn equinox with festivals and traditions. In China and Vietnam, the Mid-Autumn Festival (Moon Festival) is celebrated with mooncakes and lanterns. The pagan festival of Mabon marks the second harvest and a time of balance. In Japan, the autumn equinox (Shubun no Hi) is a national holiday for honoring ancestors. Modern celebrations include harvest festivals, apple picking, and enjoying the changing colors of fall foliage.

Related Seasonal Tools

Interested in the other seasonal transitions? Check out our First Day of Spring, First Day of Summer, and First Day of Winter calculators to find the exact dates of every equinox and solstice throughout the year.