Season Calculator
Find which season a date falls in for either hemisphere — astronomical (exact equinox and solstice times for your time zone) or meteorological — with the day of the season, days left, the next season and the year’s equinox and solstice table.
How it works
Astronomical: season = the interval between the equinox or solstice on or before the date and the next one, each placed on the calendar date it falls on in your time zone (event instants from Meeus, Astronomical Algorithms, ch. 27) · Meteorological: northern spring = Mar 1–May 31, summer = Jun 1–Aug 31, autumn = Sep 1–Nov 30, winter = Dec 1–end of Feb · Southern Hemisphere: the same intervals with the opposite names · days into the season = date − season start · days left = next season start − date
There are two common ways to date the seasons. Astronomical seasons begin at the equinoxes (around March 20 and September 22) and the solstices (around June 21 and December 21), the moments when the Sun crosses the celestial equator or reaches its farthest point north or south. Their exact instant moves by about six hours each year and resets with each leap day, so this calculator computes the real equinox and solstice times for the year with the standard astronomical algorithm (accurate to about a minute for recent centuries) and converts them to your time zone — the September 2026 equinox, for example, falls on September 22 in the Americas but on September 23 in Europe. Meteorological seasons are simply whole months grouped in threes, the convention weather services use. Pick a hemisphere and the season names flip: when it is summer in the north, it is winter in the south. Besides the season, you get the day of the season, days left, the date the next one starts, the exact season length (northern summer is the longest, about 93.6 days, because Earth moves slowest near aphelion in July), and a table of the equinoxes and solstices for this year and next.
Worked example
For September 15, 2026 in the Northern Hemisphere on US Eastern time: the June solstice fell early on June 21, 2026, and the September equinox is at 8:05 PM on September 22, 2026 (UTC−4). The date is therefore summer — 86 days into it, day 87 of 93, 92% complete — with 7 days until autumn. Under the meteorological definition the same date is already autumn (it began September 1). In the Southern Hemisphere, September 15 is late winter.
Sources: Season — Wikipedia · Earth’s Seasons: Equinoxes, Solstices, Perihelion, and Aphelion — U.S. Naval Observatory · Meeus, J. — Astronomical Algorithms, 2nd ed., chapter 27 (Equinoxes and Solstices) · Meteorological versus astronomical seasons — NOAA NCEI
Frequently asked questions
Are these astronomical or meteorological seasons?
Both — choose with the “Season definition” switch. Astronomical seasons start at the equinoxes and solstices; meteorological seasons use whole months (northern summer = June, July and August). Near a boundary the two can disagree by up to three weeks, so the calculator also shows the other definition’s season for your date.
Why does the time zone matter?
An equinox or solstice is a single instant worldwide. The 2026 September equinox is at 00:05 UTC on September 23, which is still the evening of September 22 in the Americas. The season starts on the local calendar date of that instant, so pick the zone you live in.
Why is the first day of a season not the same every year?
A calendar year is about 365.24 days, so each equinox or solstice arrives roughly six hours later than the year before until a leap day pulls it back. That is why the March equinox can be on March 19, 20 or 21 depending on the year and zone.
Why are the seasons different lengths?
Earth’s orbit is slightly elliptical. It moves fastest in early January (perihelion) and slowest in early July, so the northern summer is the longest astronomical season (about 93.6 days) and the northern winter the shortest (about 89 days).
Why do the hemispheres differ?
When the Northern Hemisphere tilts toward the Sun it is summer there and winter in the south, so the seasons are always opposite. The calculator uses the same boundary dates and swaps the names.
Is it “autumn” or “fall”?
They mean the same season; “fall” is the usual word in the United States and Canada, “autumn” elsewhere in English.
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This calculator is for educational purposes. Double-check important results before acting on them.