Last updated 3 September 2026
How the date ranges work
The Western zodiac assigns twelve signs to twelve date ranges across the year, based on where the sun traditionally sits relative to each constellation. Because that position drifts slightly year to year, different sources round the boundary dates a little differently — this tool uses the commonly cited ranges, which is the version most horoscopes and sites use.
Sun signs, moon signs and rising signs
What this tool gives you is a sun sign, which is what almost everyone means by "my star sign" and what every newspaper horoscope column is written against. It depends only on the date of birth, which is why a date is all this calculator needs.
Astrology also uses two other placements that people often confuse with it. The moon sign depends on the date and the time of birth, because the moon moves through a sign in roughly two and a half days. The rising sign, or ascendant, changes about every two hours and depends on the birth location as well as the exact time. Neither can be worked out from a date alone, which is why a full chart asks for details a sun-sign calculator does not.
Why the dates have drifted
The Western zodiac used here is the tropical zodiac, which fixes its starting point at the spring equinox rather than to the stars themselves. Because the Earth's axis wobbles slowly — a 26,000-year cycle called precession — the constellations have shifted roughly one whole sign relative to those calendar dates since the system was set down about two thousand years ago.
The practical result is that the constellation the sun sits in front of on your birthday is usually not the sign you are assigned. Both facts are true at once: the tropical zodiac is internally consistent as a calendar convention, and it no longer lines up with the sky. Astronomers also note a thirteenth constellation, Ophiuchus, which the sun passes through but which the twelve-sign system has never included.
Common questions
Why do zodiac sign date ranges vary slightly between sites?
The sun's position relative to each constellation shifts slightly year to year, so different sources round the boundary dates a little differently. This tool uses the commonly cited Western tropical zodiac ranges, which is the most widely used version.
What if my birthday falls right on a boundary date?
You're assigned whichever sign's range that exact date falls into by this tool's ranges — boundary dates are exact cutoffs here, not a blend of the two neighboring signs.
Is this based on astronomy or astrology?
Astrology — the traditional Western zodiac used in horoscopes, based on a calendar convention rather than the sun's precise current astronomical position, which has actually drifted from these date ranges over the centuries.
What is the difference between a sun sign and a rising sign?
A sun sign depends only on the birth date, which is what this tool calculates. A rising sign changes roughly every two hours and depends on the exact time and place of birth, so it cannot be worked out from a date alone.
Why is my sign different from the constellation the sun was actually in?
The tropical zodiac fixes its start at the spring equinox rather than to the stars. The Earth's slow axial wobble has shifted the constellations by about one sign over two thousand years, so the calendar dates and the sky no longer line up.
What about Ophiuchus, the thirteenth sign?
The sun does pass in front of the Ophiuchus constellation, which is an astronomical fact. The Western zodiac has always used twelve equal segments as a calendar convention rather than mapping the constellations directly, so it has never included it.