Sidereal chart calculator: your Vedic birth chart

Both zodiacs cut the ecliptic, the Sun's yearly path across the sky, into twelve signs of 30 degrees. They differ only in where they start counting. The tropical zodiac of Western astrology starts at the March equinox, the moment the Sun crosses the celestial equator heading north, so its signs stay tied to the seasons. The sidereal zodiac of Vedic astrology, or Jyotish, starts from a point fixed against the stars, so its signs stay lined up with the star groups they are named after.

On the Lahiri definition the two starting points coincided around the end of the third century. They have drifted apart ever since, because the equinox itself moves, and that drift is what the sidereal chart corrects for.

The Earth's axis wobbles like a slowing top and traces a full circle in the sky roughly every 25,800 years. As it turns, the March equinox slides backward along the zodiac by about 50 arcseconds a year. The tropical zodiac moves with the equinox; the sidereal zodiac stays with the stars.

The distance between them is the ayanamsa, the precession piled up since the two last matched. On 1 January 2026 it stood at 24°13′, and the table above lists the engine's value for other years, from 1900 to 2050.

Several ayanamsas exist. Each pins sidereal 0° Aries to a slightly different star or date, and they disagree by up to a few degrees. Lahiri, also called Chitrapaksha, is the one India's Calendar Reform Committee settled on in the 1950s for the national calendar, and it is the default in most Vedic software. It places the bright star Spica, Chitra in Sanskrit, at 0° Libra.

This calculator uses the true Lahiri value as the committee defined it, 23°15′00.658″ on 21 March 1956, carried forward with precession and nutation. The site's test suite checks it against published values to within two arcseconds.

Every planet, the ascendant and the Midheaven move back by the same amount, the ayanamsa for your birth moment. A placement in roughly the first 24 degrees of a tropical sign falls back into the sign before it; one in the last six degrees stays where it is. So about four placements in five change sign. A Sun at 10° Taurus becomes a sidereal Sun near 16° Aries, while a Sun at 28° Taurus stays in Taurus at about 4°.

What does not move is the shape of the chart. The whole wheel rotates as one, so the angles between planets, the aspects and the Placidus houses are identical in both zodiacs. Whole-sign houses are the exception: they follow the sign on the ascendant, so when your rising sign changes, every whole-sign house boundary changes with it.

Vedic astrologers usually draw the chart as a square, in the North or South Indian style, and read it with whole-sign houses, the Moon's nakshatra and the planetary periods called dashas. This calculator draws a round Western wheel and does not interpret nakshatras or dashas, so treat it as the sidereal positions a Jyotish reading starts from: signs, degrees and houses.

To match the Vedic convention, set the house system to whole sign. The record under the wheel then lists every planet with its sidereal sign, degree and house, and a share link keeps the zodiac and house settings you chose.

Neither one is a measuring error. The tropical zodiac follows the seasons, the Sun's relation to the Earth; the sidereal zodiac follows the stars behind the Sun. Neither matches the constellations exactly, since real constellations are unequal in size and the official astronomical boundaries put the Sun in Ophiuchus from late November to mid December.

Many people keep both: the tropical chart for Western psychological astrology, the sidereal chart for Jyotish technique. The calculator switches between them for the same moment, so you can see which of your placements move and which stay.