This is the single most common message we receive, so it deserves a proper answer rather than a footnote.

Two zodiacs, both real

A zodiac needs a starting point — some agreed place to call zero degrees of Aries. Two different choices have been made, and both are internally consistent.

The tropical zodiac, used in Western astrology and in newspaper columns, starts at the spring equinox: the moment the Sun crosses the celestial equator going north. That moment defines zero Aries by definition.

The sidereal zodiac, used in Jyotish, starts from a fixed point among the stars. Zero Aries is a place in the sky, not a moment in the year.

Why they have drifted apart

The Earth's axis wobbles, completing one slow circle every 25,772 years. This is called the precession of the equinoxes, and it means the spring equinox slides backwards through the constellations at about 50 arcseconds a year — a degree every 72 years.

The two zodiacs agreed around the fifth century CE. Since then they have separated by roughly 24 degrees. Twenty-four degrees is most of a sign, which is why so many people find their sign shifts by one when they move from one system to the other.

What ayanamsa means

The gap between the two starting points is the ayanamsa. It is not a fudge factor; it is a measured quantity that grows every year. On this site the default is the Lahiri ayanamsa, the standard adopted by the Government of India's Calendar Reform Committee, and it is applied to every calculation.

You can see the exact value for any moment on the panchang page. As of now it is a little over 24 degrees.

Which one is correct

Neither, in the sense you might want. They are two conventions for slicing the same sky. A tropical chart and a sidereal chart of the same birth are both arithmetically correct; they disagree because they measure from different origins.

What matters is consistency. A reading built on sidereal positions has to be interpreted with sidereal rules, and Jyotish is a sidereal system. Mixing a sidereal chart with tropical interpretations, or the reverse, produces something that belongs to no tradition at all.

So your sign has not changed

The Sun was where it was at your birth. Only the ruler being held up against it is different. If you want to see both, calculate a chart here and set the ayanamsa to "Tropical" in the advanced settings — you will get the Western positions from the same engine.