☀ Free Equinox & Solstice Calculator — Exact Dates and Times
Umbriel's free season calculator gives the exact moment of each equinox and solstice — solved from the Sun's real position, in your own timezone. Free, no account.
- What you'll needNothing
- What you getAll four turns of the Sun's year, dated to the minute in your timezone
- CostFree — no account required
Runs in your browser. Nothing to install, nothing to set up.
What it actually is
An equinox is not a date somebody agreed on. It is the instant the Sun's apparent longitude reaches exactly 0° — and the solstices are 90°, 180° and 270°. Umbriel solves for that instant rather than looking it up.
That is why the date can differ by a day depending on where you are: the moment is a single instant worldwide, and your calendar date for it depends on your timezone. The page gives it in yours.
⚠️ The four are not evenly spaced, and the figures here show it rather than rounding it away. The Earth moves faster when it is closer to the Sun, so the seasons genuinely differ in length by a couple of days.
This is the sky's oldest calendar — the one every tradition in the world built its festivals on before anyone had a chart.
In chart terms the four moments are the Sun entering Aries, Cancer, Libra and Capricorn — the cardinal ingresses — which is why they are also read as the opening of a season in mundane astrology, and why an eclipse or a station falling close to one tends to get extra weight. The dates here are the same instants that anchor Umbriel's year-ahead timeline, computed once and shared rather than worked out twice.
How Umbriel computes it
An equinox or a solstice is not a date somebody chose; it is the instant the Sun's apparent longitude reaches exactly 0°, 90°, 180° or 270°. Umbriel solves for that instant from the same engine that casts the charts and reports it to the minute in your own timezone, which is why the date can differ by a day from a calendar printed for a different part of the world. The gaps between them are not equal — the Earth moves faster at perihelion — so the four seasons genuinely differ in length by a couple of days, and the figures here show it rather than rounding it away. The solve is a Newton iteration on the Sun's own longitude rather than a lookup, converging to well under a second of arc, which is far finer than the minute the result is displayed to. That also means any year works — there is no table to run out, forward or back — and the same code path produces the season markers used on the year-ahead timeline, so the two pages cannot disagree with each other.
What's in your result
- All four, to the minuteSolved from the Sun's real longitude, not a stored table.
- In your timezoneSo the date is the date where you are.
- Any yearForward or back, not just this one.
- The unequal gapsShown rather than smoothed — the seasons really are different lengths.
Common questions
When is the next equinox?
Umbriel solves for it live and gives the exact moment in your own timezone, for whichever year you are looking at.
Why do sites give different dates?
Because it is a single worldwide instant, and which calendar date it falls on depends on your timezone.
Are the seasons the same length?
No. The Earth moves faster near perihelion, so they differ by a couple of days, and the figures here show it.
What defines an equinox exactly?
The instant the Sun's apparent longitude reaches 0° (spring) or 180° (autumn). The solstices are 90° and 270°.
Is the equinox calculator free?
Yes, and it needs no birth details at all.
Go deeper
Each of these is a free tool in its own right.
Umbriel offers every system here as a set of prompts to think with, never as a statement of fact about who you are. Take what's useful, leave the rest.