How we calculate

Where the positions come from

Every planet position starts from the JPL DE440 ephemeris, a public numerical model of the Solar System used by space missions. We read it with CSPICE, the toolkit published for this purpose. Dates and times are converted to a single universal time scale before any lookup, so a birth time in any time zone, including historic daylight-saving changes, is handled in one place.

The Moon's nodes, Rahu and Ketu, are the mean nodes. They are points on the sky, not bodies.

Zodiac and houses

Indian astrology uses the sidereal zodiac. We subtract the Lahiri (Chitrapaksha) ayanamsa from the tropical longitude, which today is about 24 degrees. Houses are whole-sign: the rising sign is the first house, the next sign the second, and so on. See ayanamsa and lagna.

Panchang

Tithi, nakshatra, yoga and karana are worked out from the Sun's and the Moon's longitudes. Sunrise, sunset and Rahu Kalam are calculated for the place you choose. See panchang.

Interpretation rules

Yogas, doshas, dasha periods and the 36-point match follow written rules based on the classical Parashari texts. The report text is a library of explanations that are selected by those rules for your chart. Each statement is tied to a placement in your chart, and the reports say when a rule is cancelled or only partly applies.

How we check our work

The engine exists as two independent implementations, and our test suite compares them on hundreds of generated charts, with the tolerances written down: planet and ascendant longitudes within 0.01 degree, the ayanamsa within 0.001 degree, and signs, nakshatras, panchang numbers and dasha lords exactly equal.

This shows that the implementations agree with each other. It is not a certificate of agreement with every other astrology program. We are comparing our results with other established software and trusted reference charts, and where small differences remain, for example in how a dasha year is counted, we will state the convention we use. We do not publish an accuracy figure until that comparison supports it.

What we do not claim

• We do not claim that astrology predicts events, health, money or legal outcomes.
• We do not claim exactness beyond what the inputs allow. A birth time that is off by minutes can change the rising sign and divisional charts.
• Where traditions differ, for example the exaltation signs of Rahu and Ketu or the houses counted for Mangal dosha, we pick one and say which.