Autumn 2025: When is autumn equiniox date, what is it, meaning, plus start and end dates of autumn season

The autumn equinox is upon us - and no matter which of two seasonal calendars you follow, that means the season of Autumn is pretty much here too. The days are getting shorter, the nights are getting longer, the weather is turning, and it’s time to find the blankets again.

We've all become accustomed to experiencing such dark and dreary weather in autumn and - begrudingly - accept it. In addition, we all know, of course, that in the UK the clocks are turned back every October to mark the end of British Summer Time. This also brings with it much shorter days and longer nights. But, the official start of autumn actually comes much sooner than this date.

So, when exactly does autumn start and what is the autumn equinox? Here’s everything you need to know.

When does autumn begin?

There are actually two ways of calculating the first day of autumn, depending on whether you follow the meteorological or definitions of the seasons. But, whichever one you follow, both happen in September. In 2025, meteorological autumn begins first, on Monday September 1, followed by astronomical autumn on Monday September 22.

What’s the difference between meteorological autumn and astronomical autumn?

These are the key differences between meteorological autumn and astronomical autumn, and how the date of each is determined.

Meteorological autumn

The meteorological autumn date is the easiest to work out. It is based on the simple principle that the year is split into four seasons, and that each of these seasons are made up of three full months, as per the Gregorian calendar. This definition makes it easier to compare seasonal and monthly statistics, and means that every season starts on the same date every year.

This means that every year autumn begins on 1 September and lasts until 30 November, with winter then starting on 1 December. In this instance, summer ends of 31 August.

Astronomical autumn

The astronomical season is less straightforward to work out as it can change every year. This is because it starts on the date of the autumn solstice, also known as the autumn equinox or the September equinox, which comes later in September but can vary slightly from year on year.

In 2025, the autumn solstice falls on Monday 22 September, which is the same date as last year. In this instance, summer will end on Sunday 21 September. It can, however, occur on any date between 21 and 24 of the month, although 22 September is the most common date for it to occur.

The astronomical autumn then lasts until another changeable date, the winter solstice, the shortest day of the year, which is set to take place on Sunday 21 December this year. The number of daylight hours on the shortest day will be 7 hours, 49 minutes and 42 seconds. That’s 9 hours, 41 minutes shorter than the summer solstice, when daylight hours are at a maximum.

What is the autumn equinox?

Equinoxes take their name from the Latin for equal night. They happen twice a year, at the start of spring and autumn, and mark the moment the Earth’s equator passes directly through the centre of the sun’s path. On each of these days, the planet should get 12 hours of daylight and 12 hours of darkness, although this is complicated somewhat  by the Earth’s atmosphere and weather conditions affecting the way we see sunlight.

The autumn equinox can occur at any time between 21 and 24 September, and marks the start of autumn - if you follow the astrological definitions of the seasons. This year, the autumnal equinox will occur on Sunday 22 September at around 1.42pm UK time.

When will autumn end?

There are also two ways of calculating the last day of autumn. According to the metrological measure of the seasons, the last day of autumn this year will be Sunday 30 November, with winter then starting on Monday 1 December. But, the astrological measure of the seasons states that the last day of autumn 2025 will be on Sunday 21 December, followed by the first day of winter on Monday 22 December.