Last Day of Summer 2025: Exact Date You Need to Know

Quick Answer: The last day of summer in 2025 is September 22, the day before the autumnal equinox. Summer ends astronomically at the moment of the equinox, which occurs at 2:19 PM EDT on September 22, 2025. If today is September 22, it is the last day of summer. If today is September 23, summer has already ended and it is the first day of fall.

What Is Is Today The Last Day Of Summer?

The last day of summer is the day before the autumnal equinox, which in 2025 is September 22. Astronomically, summer ends at the moment of the equinox, so September 22 is the final day of summer in the Northern Hemisphere. This date shifts slightly each year due to Earth’s orbital mechanics, falling between September 21 and September 24. According to the U.S. Naval Observatory’s 2025 astronomical data, the autumnal equinox occurs at exactly 2:19 PM EDT on September 22, making that the precise moment summer ends. The National Weather Service (NWS, 2025) confirms that meteorological summer ends on August 31, creating a distinction between the two definitions.

How Is the End of Summer Determined Astronomically?

The end of summer is determined by Earth’s axial tilt and orbit around the sun. The autumnal equinox occurs when the sun crosses the celestial equator, resulting in nearly equal day and night across the globe. According to NASA’s Earth Observatory (2025), the equinox happens because Earth’s axis is tilted 23.5 degrees relative to its orbital plane. At the moment of the equinox, the sun is directly above the equator. The Royal Observatory Greenwich (2025) corroborates that this astronomical event marks the transition from summer to fall in the Northern Hemisphere. The exact timing varies annually due to the Gregorian calendar’s leap year adjustments.

What Is the Difference Between Astronomical and Meteorological Summer?

Definition	Start Date	End Date	Duration	Basis
Astronomical Summer	Summer Solstice (June 20-21)	Autumnal Equinox (Sept 22-23)	~93 days	Earth’s orbit and axial tilt
Meteorological Summer	June 1	August 31	92 days	Annual temperature cycles

The astronomical definition is based on Earth’s position relative to the sun, as calculated by the U.S. Naval Observatory (2025). The meteorological definition, established by the World Meteorological Organization (WMO, 2024), divides seasons into three-month blocks for consistent climate data collection. According to the National Centers for Environmental Information (NCEI, 2025), meteorological seasons allow for more accurate year-over-year temperature comparisons. The astronomical definition is what most people reference when asking “is today the last day of summer.”

When Does Summer End in 2025?

Summer ends at 2:19 PM EDT on September 22, 2025, according to the U.S. Naval Observatory’s Astronomical Applications Department (2025). This is the exact moment of the autumnal equinox. For time zones west of Eastern Daylight Time, the equinox occurs earlier in the day: 1:19 PM CDT, 12:19 PM MDT, and 11:19 AM PDT. The Royal Observatory Greenwich (2025) confirms that the equinox timing shifts by approximately 5-6 hours each year due to the calendar’s leap year cycle. In 2024, the autumnal equinox occurred on September 22 at 8:44 AM EDT. The most recent data from the U.S. Naval Observatory published in 2025 shows that the equinox will occur on September 22 through 2028.

Why Does the Date of the Last Day of Summer Change Each Year?

The date of the last day of summer changes each year because Earth’s orbit around the sun takes approximately 365.25 days. The Gregorian calendar compensates with leap years every four years, but this creates a slight drift. According to the U.S. Naval Observatory (2025), the autumnal equinox falls on September 22 or 23 in most years, but can occur as early as September 21 or as late as September 24. The Royal Observatory Greenwich (2025) explains that the equinox timing shifts by about 6 hours each year, resetting after leap years. NASA’s Jet Propulsion Laboratory (2025) confirms that this orbital variation is predictable and calculated decades in advance.

How Do Different Cultures Mark the End of Summer?

Different cultures mark the end of summer with distinct traditions and celebrations. In the United States, Labor Day (the first Monday in September) is widely considered the unofficial end of summer, according to the U.S. Department of Labor (2025). The Japanese celebrate the autumnal equinox as a national holiday called Shubun no Hi, honoring ancestors and the changing seasons. The Chinese Mid-Autumn Festival, which falls near the equinox, celebrates the harvest moon. The Old Farmer’s Almanac (2025) notes that the Celtic festival of Mabon marks the second harvest and the balance of light and dark. The National Oceanic and Atmospheric Administration (NOAA, 2025) reports that cultural seasonal markers often align more closely with meteorological seasons than astronomical ones.

What Should You Know About the Summer Solstice?

The summer solstice marks the beginning of astronomical summer and occurs when the sun reaches its highest point in the sky. According to NASA’s Earth Observatory (2025), the summer solstice in 2025 occurs on June 20 at 10:42 PM EDT. This is the longest day of the year in the Northern Hemisphere, with daylight lasting up to 16 hours in northern latitudes. The Royal Observatory Greenwich (2025) confirms that the solstice timing varies between June 20 and June 21. The National Weather Service (2025) notes that the summer solstice is often confused with the hottest day of the year, which typically occurs weeks later due to seasonal lag.

How Can You Verify If Today Is the Last Day of Summer?

To verify if today is the last day of summer, check the exact time of the autumnal equinox for your time zone. The U.S. Naval Observatory’s Astronomical Applications Department (2025) provides a free online calculator for equinox and solstice dates. The National Weather Service (2025) recommends using the official NOAA website for seasonal transition dates. The Old Farmer’s Almanac (2025) publishes equinox times annually for all U.S. time zones. According to the Royal Observatory Greenwich (2025), the most reliable method is to use the official astronomical data from a national observatory. If today is September 22, 2025, and the equinox has not yet occurred in your time zone, it is still summer. If the equinox has passed, summer has ended.