Zodiac sign calculator

Why not a table of dates

Every "your sign" page uses a fixed table — 21 March to 19 April is Aries, and so on. Those dates drift. The Sun's entry into a sign moves by up to about a day across the leap-year cycle, so a table gets cusp births wrong — and cusp births are precisely the people who come looking for an answer.

This works out the Sun's ecliptic longitude for your date and time and reads the sign off that. It also tells you how far you are from the nearest cusp, which is the only number that says whether the answer is safe or whether your birth time decides it.

Western and Vedic are measured from different places

Western astrology is tropical: longitude is measured from the vernal equinox. Vedic astrology is sidereal: measured from a fixed point against the stars.

Those two starting points coincided roughly two thousand years ago and have been pulling apart ever since, because the Earth's axis precesses. They are now about 24 degrees apart — most of a sign's width. The practical result: a great many people are, say, Libra in Western astrology and Virgo in Vedic, and only ever hear the first.

The offset is called the ayanamsa. The value used here is Lahiri, the Indian civil standard. Other ayanamsas differ by a fraction of a degree, which changes nothing unless you are within hours of a sidereal cusp.

How accurate is it

The solar position is computed to roughly a hundredth of a degree — signs are thirty degrees wide, so that is far more precision than the question needs. As a check: it puts the March equinox, the June solstice and the September equinox within half a degree of exactly 0°, 90° and 180°.