Calculation methodology

Ephemeris

Planetary positions are computed with the Skyfield library from NASA JPL's DE421 ephemeris, which covers 1900 to 2050. Dates outside that range are rejected rather than estimated. Rahu is the mean lunar node; Ketu is exactly opposite.

Time and place

Birth places are resolved to latitude, longitude and an IANA time zone. Local birth time is converted to Universal Time using that zone's historical rules, including daylight saving and India's 1942–45 war time (UTC+6:30). When the birth time is unknown we calculate for 12:00 and hide time-sensitive results.

Zodiac and ayanamsa

Sidereal zodiac with the Lahiri (Chitrapaksha) ayanamsa, computed by fixing the star Spica (Chitra) at 180°. Our ayanamsa can differ from other Lahiri implementations by up to about one arc-minute; that can move Moon-based end times (Nakshatra, Tithi) by a few minutes relative to other almanacs.

Lagna and houses

The Ascendant is the sidereal ecliptic longitude rising at the birth place. Houses are whole-sign: the Lagna's sign is the first house. We don't currently show a Bhava Chalit chart.

Nakshatra and Dasha

Nakshatras are 27 equal divisions of 13°20′ from 0° sidereal Aries; padas are 3°20′. The Vimshottari Dasha starts with the lord of the Moon's Nakshatra, with the first period's balance proportional to the part of the Nakshatra still to be crossed. Dasha years are Gregorian years of 365.2425 days; some almanacs use 360-day or 365.25-day years, which shifts dates slightly.

Divisional charts

D2 (Hora), D3 (Drekkana), D9 (Navamsa), D10 (Dashamsa) and D60 (Shashtiamsa) use the Parashari division rules. Vargottama means the same sign in D1 and the varga.

Panchang

• The day runs sunrise to sunrise; sunrise and sunset are computed for the place's coordinates.
• Tithi, Nakshatra, Yoga and Karana end times are found by numerically searching for the moment the Sun–Moon angle or the Moon’s longitude crosses each boundary (accurate to about a second).
• Months are labelled Purnimanta or Amanta according to the region of the place (Amanta for much of western and southern India).
• Rahu Kaal, Yamaganda and Gulika are eighths of daytime by weekday; Abhijit is the eighth of fifteen daytime muhurtas; Choghadiya divides day and night into eight parts; Hora divides each into twelve.
• Festival dates apply classical Tithi-at-sunrise rules. Regional practice can differ.

Doshas and yogas

Mangal Dosha checks Mars in houses 1, 2, 4, 7, 8 or 12 counted from the Lagna, the Moon and Venus, and notes common mitigations. Kaal Sarp checks whether all seven planets lie on one side of the Rahu–Ketu axis. Sade Sati is Saturn transiting the 12th, 1st and 2nd signs from the natal Moon. Yogas are detected with explicit rules (for example, Gaja Kesari: Jupiter in a kendra from the Moon). These rules vary between texts; we show the rule used next to each result.

Kundli matching

Ashtakoot Guna Milan uses the standard 36-point tables from both partners' Moon sign and Nakshatra, with the classical exceptions for Nadi, Bhakoot and Gana doshas listed when they apply.

AI astrologer

The AI model receives only a structured summary of your calculated chart and is instructed not to state any placement or date outside it, to avoid the Ascendant and houses when the birth time is unknown, to separate calculated facts from interpretation, and not to promise outcomes or recommend paid remedies. It can still make mistakes; the chart itself is the source of truth.

Testing

Automated tests cover Nakshatra and pada boundaries, Dasha transitions, house placement, date and time validation, daylight-saving conversions and Hora sequences, using real engine output as fixtures. Found a discrepancy? Tell us.