Sun sign
Hidden card – fill in your birth data to reveal it
Zodiac sign calculator: what is my sign?
Your zodiac sign is the sign the Sun was in when you were born. For most birthdays the date alone is enough. If you were born on a boundary date, the exact moment the Sun changed sign that year decides it, so add your birth time and place.
Hidden card – fill in your birth data to reveal it
- Updated
- How we calculate it
- Computed on your device
We calculate the Sun’s position for your birth moment instead of looking it up in a table of typical dates, so boundary birthdays come out right.
If your Sun is within one degree of the next sign, we say so – a few hours of birth time can then make the difference.
How we calculate it
Planet positions come from Astronomy Engine, an open-source astronomy library (MIT license) whose author documents an accuracy of about ±1 arcminute. We use apparent geocentric positions on the true ecliptic of date (IAU 2006 precession and IAU 2000B nutation, with light-time and aberration) – the same definition most astrology software uses.
Your local birth time is converted to Universal Time with the historical rules of the IANA time zone database, including past daylight-saving changes and war-time clocks. City coordinates and time zones come from GeoNames. If a time was skipped or repeated because the clocks changed, we tell you instead of guessing silently. One honest limit: for births before about 1970 the database is not guaranteed to be complete, and a small town may have kept a different local time than the reference city of its zone. We always show the UTC offset we applied, so you can compare it with what you know (for example a time on a birth certificate).
We test the engine against NASA/JPL Horizons (DE441) for reference birth data: planets agree within 1 arcminute and the Moon within 2; the Ascendant and Midheaven, computed from Horizons sidereal time, agree within 3 arcminutes.
Everything runs in your browser. Your birth data is not sent to a server and nothing is stored.
Why date tables are sometimes wrong
The Sun enters each sign at a slightly different time every year, and the calendar date of that moment depends on your time zone. A table with fixed dates can therefore be off by a day for people born on the boundary.
Questions
What zodiac sign am I if I was born on the cusp?
You have one Sun sign – the one the Sun was in at your birth moment. Enter your birth time and place and the calculator settles it.
Do I need my birth time?
Only if you were born on a boundary date. For every other day of the year the date is enough.
Is the zodiac sign the same as the constellation?
No. Tropical signs are 30° sections counted from the March equinox; the constellations with the same names are star patterns that today lie roughly one sign further along.
Sources
- Astronomy Engine (Don Cross) – source code and documentation, MIT license
- NASA/JPL Horizons System – reference ephemerides used to test our results
- IANA Time Zone Database (tz database) – historical time zone and daylight-saving rules
- GeoNames geographical database (CC BY 4.0) – city coordinates and time zones
- Encyclopaedia Britannica – Zodiac
Astrology, numerology and the Chinese zodiac are offered for entertainment and self-reflection. They are not scientifically validated and are not a substitute for professional advice (medical, psychological, legal or financial). Astronomical positions are calculated precisely; interpretations are traditional symbolism, not predictions.