Many people love autumn. Not me — I’ve hated it since about 2016, and I wrote a whole post about it if you want the full rant. But if you’re one of those people counting down the days to cosy jumpers and pumpkin spice everything, this is for you.
The short answer: it depends which definition you use. Meteorological autumn starts on 1 September every year. Astronomical autumn starts around 22 or 23 September, with the exact date and time shifting slightly each year. In the UK, most of us tend to feel it somewhere in between. The mornings get colder in early September, the leaves start turning in October, and by November it’s definitely, miserably autumn.
Here’s a closer look at how the different systems work.
Autumnal Equinox
The Autumnal Equinox marks the start of autumn, when day and night are nearly equal in length. This phenomenon occurs due to the Earth’s axial tilt, positioning the equator directly under the sun.
Dates for Northern and Southern Hemispheres
Autumn marks a significant time of year in both the Northern and Southern Hemispheres. The equinox heralds its arrival. Here are the crucial dates for these regions.
| Hemisphere | Meteorological Autumn Starts | Astronomical Autumn Starts (approx.) |
|---|---|---|
| Northern Hemisphere (UK) | 1 September | 22–23 September |
| Southern Hemisphere | 1 March | 20–21 March |
Equinoxes mark a period when day and night are of almost equal length. Yet, they don’t bring exactly 12 hours of daylight and 12 hours of darkness. This variation arises because of how sunrise and sunset times change.
In the UK, the equinox lands on 22 or 23 September. That’s because a full year of seasons is roughly 365 days and 6 hours long, so the equinox happens about six hours later each year, then jumps back again after a leap year. In 2024 and 2025 it was on 22 September, and in 2026 it moved to 23 September.
Understanding these dates and times helps us welcome the season more accurately.
Astronomical vs. Meteorological Autumn
Astronomical autumn is determined by the position of Earth’s axis and lasts for about 89 days, whereas meteorological autumn is based on temperature and always runs for the three full months of September, October and November.
Definitions and Differences
Astronomical seasons depend on Earth’s position relative to the sun. This system considers events like equinoxes and solstices to mark the beginning and end of seasons. For instance, astronomical autumn starts between 22 or 23 September and wraps up on 21 or 22 December in the Gregorian calendar.
Leap years can cause slight changes in these dates.
Meteorological seasons, however, follow the annual temperature cycle and are split into full months based on the meteorological system. Meteorological autumn aligns with cooler temperatures from 1 September to 30 November every year.
These dates stay consistent, making weather forecasting more straightforward for entities like the Met Office. Unlike astronomical seasons, this method does not adjust for leap years since it relies on average monthly temperatures rather than direct sunlight positions or Earth’s tilt degrees.
So, When Does Autumn Actually Start?
For most practical purposes in the UK: 1 September if you’re going by weather patterns, or 22/23 September if you’re going by the astronomy. The Met Office uses 1 September. Most people’s gut feeling lands somewhere in between — that first cold morning in early September, usually.
Either way, it’s coming. Sorry. If you’re going to make the most of it anyway, here are my favourite things to do in North Yorkshire in autumn.
FAQs
When does autumn officially start in the UK? There are two answers. Meteorologically, autumn starts on 1 September, which is the date the Met Office uses, based on temperature patterns. Astronomically, it starts with the autumnal equinox, which falls on 22 or 23 September each year. Both are correct; they’re just measuring different things.
What’s the difference between meteorological and astronomical autumn? Meteorological autumn (1 September – 30 November) is based on average temperatures and is consistent every year, which makes it useful for weather forecasting. Astronomical autumn is based on the Earth’s position relative to the sun and starts at the equinox — when day and night are roughly equal length. It varies slightly year to year.
When is the autumn equinox in 2026? The autumnal equinox in 2026 was on Wednesday 23 September at 1:06am BST. In 2024 it was 22 September at 13:43 BST, and in 2025 it was 22 September at 19:19 BST.
Why do some people say autumn starts in August? They’re not entirely wrong. Some phenological definitions of autumn start when the first leaves begin to turn and the average daily temperature drops below certain thresholds, which can happen in late August in the UK.
Does the whole UK experience autumn at the same time? Not exactly. Scotland and northern England tend to feel autumn earlier than southern England, as the nights get colder sooner and the leaves turn earlier. The south can still feel like late summer in early September while the north is already reaching for a jacket.
What’s the first day of autumn 2026 in the UK? Meteorologically, 1 September 2026. Astronomically, 23 September 2026. Take your pick, either way summer is over.