Seasons Calculator
In the Northern Hemisphere in 2026, astronomical fall starts September 23 UTC and winter starts December 21 UTC. This seasons calculator lists all four season starts for an integer year from 1000 through 3000. Choose astronomical dates based on equinox and solstice instants or meteorological dates fixed to March 1, June 1, September 1, and December 1. Hemisphere changes the season names, not the underlying four event dates.
Quick answer
Astronomical seasons begin at the equinoxes and solstices, which shift by a day or so each year.
What this tells you
- •Astronomical seasons begin at the equinoxes and solstices, which shift by a day or so each year.
- •Meteorological seasons begin on fixed dates: the first of March, June, September, and December.
- •The Southern Hemisphere has opposite seasons, so its spring starts when the north begins fall.
- •Astronomical dates are shown in UTC and can fall a day earlier or later in your local time.
- •The astronomical result includes a UTC time as well as a date.
- •The supported year must be a whole number from 1000 through 3000.
- •Northern spring and Southern fall begin at the same March equinox instant.
- •Meteorological results have no event time because each season begins at the start of a fixed calendar day.
How to Use
- 1Enter a whole-number year between 1000 and 3000.
- 2Choose Northern or Southern Hemisphere. This assigns the correct season name to each equinox or solstice.
- 3Choose astronomical dates for solar events or meteorological dates for fixed three-month groupings.
- 4Read all four results in chronological order from March through December.
- 5For astronomical results, treat the displayed date and time as UTC and convert to your local zone if the local calendar date matters.
- 6For meteorological results, remember that the four dates stay fixed every year.
How It Works
Formula
astronomical season start = equinox or solstice instant, meteorological = fixed first of the monthAstronomical mode calculates the March equinox, June solstice, September equinox, and December solstice with the Meeus periodic-term method and converts each Julian day to UTC. The implementation is intended for years 1000 through 3000. Meteorological mode does not calculate solar position. It assigns March 1, June 1, September 1, and December 1. Northern event names are Spring, Summer, Fall, Winter in that order. Southern names are Fall, Winter, Spring, Summer for the same four dates.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
When does fall start in 2026?
In 2026 the September equinox lands on the 23rd in UTC, which marks the astronomical start of fall in the Northern Hemisphere.
When does winter start in 2026?
The December solstice in 2026 falls on the 21st, the shortest day of the year and the astronomical start of winter in the north.
Southern Hemisphere astronomical seasons in 2026
The equinox and solstice dates match the northern list, but the season names reverse. The March equinox begins southern fall and the December solstice begins southern summer.
Northern meteorological seasons in 2026
Meteorological mode uses fixed month boundaries. It does not use the equinox or solstice date and therefore gives the same month and day in every supported year.
Which season a trip falls in: Iceland, September 20 to 27, 2026
Marcus is flying to Reykjavik for September 20 to 27, 2026 and wants to know whether to pack for summer or fall. The astronomical result puts the September equinox at 00:06 UTC on September 23, 2026, and Iceland keeps UTC all year, so his first three days are the last of astronomical summer and fall begins six minutes after midnight on the 23rd. Switching the calendar to meteorological puts the whole trip in fall, which started September 1. In New York the same instant is 8:06 pm on September 22, so a list of equinox dates written for US readers may say the 22nd.
Astronomical vs meteorological seasons, Northern Hemisphere, 2025 to 2027
Season starts as this calculator computes them, with the fixed meteorological dates beside each one. The astronomical column is the UTC calendar date of the equinox or solstice.
| Year | Season | Astronomical start (UTC) | Meteorological start |
|---|---|---|---|
| 2025 | Spring | Mar 20 | Mar 1 |
| 2025 | Summer | Jun 21 | Jun 1 |
| 2025 | Fall | Sep 22 | Sep 1 |
| 2025 | Winter | Dec 21 | Dec 1 |
| 2026 | Spring | Mar 20 | Mar 1 |
| 2026 | Summer | Jun 21 | Jun 1 |
| 2026 | Fall | Sep 23 | Sep 1 |
| 2026 | Winter | Dec 21 | Dec 1 |
| 2027 | Spring | Mar 20 | Mar 1 |
| 2027 | Summer | Jun 21 | Jun 1 |
| 2027 | Fall | Sep 23 | Sep 1 |
| 2027 | Winter | Dec 22 | Dec 1 |
Astronomical dates come from the tool's own calculation, the periodic-term method in Meeus, Astronomical Algorithms, chapter 27, and are shown as UTC calendar dates. The reference values for equinox and solstice instants are the ones published by the US Naval Observatory and tabulated in The Astronomical Almanac. The meteorological convention of March 1, June 1, September 1, and December 1 follows NOAA's National Centers for Environmental Information. Southern Hemisphere season names are reversed on the same dates.
Why local dates can differ from UTC
An equinox or solstice is one worldwide instant, but clocks display that instant differently by time zone. An event late on one UTC date may already be the next calendar day east of the prime meridian or still the previous day farther west.
Meteorological seasons avoid that issue because they are date-based groupings rather than calculated instants. Their fixed boundaries are useful for monthly climate records, but they do not claim to identify the exact solar event.
Hemisphere selection changes seasonal interpretation. The September equinox begins northern fall and southern spring at the same instant, so both results are correct for their location.
The astronomical dates carry three limits. The instants are the tool's own calculation using the periodic-term method from Meeus, Astronomical Algorithms, chapter 27, which the implementation documents as accurate to about a minute for years 1000 through 3000. It does not apply the Delta T offset between Terrestrial Time and UTC, so a displayed time can sit a minute or so from the instant the US Naval Observatory publishes and The Astronomical Almanac tabulates. A minute rarely changes the date, but an event within a minute of midnight UTC could land on the neighboring day.
Calendar dates also move by up to a day between years and between time zones. The December solstice above falls on December 21 in 2026 and December 22 in 2027, and the 2026 September equinox at 00:06 UTC on September 23 is still 8:06 pm on September 22 in New York. The Southern Hemisphere reverses the names, so the same March instant begins fall in Sydney and spring in Chicago. None of this describes local climate. NOAA's National Centers for Environmental Information explains that meteorological seasons were fixed to whole months to follow the annual temperature cycle and make seasonal statistics easier to compare, and neither calendar here reflects monsoon, wet and dry, or polar seasons.
Common mistakes
- Assuming seasons always start on the same date. Astronomical season dates shift by a day or two each year because the equinoxes and solstices do.
- Mixing up the two calendars. Meteorological fall starts September 1, while astronomical fall starts at the September equinox around the 22nd or 23rd.
- Forgetting the hemisphere. When it is fall in the north it is spring in the south, so the same date marks opposite seasons.
- Reading the UTC astronomical date as a guaranteed local date without applying the location's time-zone offset.
- Entering a decimal year. The implementation accepts whole years only.
- Treating astronomical and meteorological systems as competing corrections when they answer different calendar conventions.
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