Methodology

How we calculate your Vedic chart

The formulas, time zone rules and checks behind this calculator. Every step follows a published standard, and the results were compared with Swiss Ephemeris on 22,001 charts.

What we calculate and where

Everything runs in your browser. Your birth date, time and city are never sent to a server and never stored. There's no sign-up and no email, and all the calculations happen on your device.

The zodiac: Lahiri ayanamsa

To convert tropical positions to the sidereal zodiac, we compute the Lahiri ayanamsa, the angular gap between the Western and the sidereal zodiac. We anchor the value at 23°15′00.658″ on March 21, 1956, at 0:00 Terrestrial Time, the Indian Astronomical Ephemeris definition used since 1985. From that epoch, the mean value grows with the general precession in longitude of the IAU 2006 precession model, about 50 seconds of arc a year.

We then add nutation in longitude, so it's the true ayanamsa rather than the mean value. Each body's sidereal longitude equals its apparent tropical longitude minus the true ayanamsa, wrapped to 360°. This gives an ayanamsa of 23°09′ on January 1, 1950, 23°51′ on January 1, 2000, and 24°14′ in October 2026.

Planets, nodes and the lagna

Apparent tropical positions for the Sun, Moon, and five visible planets come from astronomy-engine, an open-source astronomy library. Rahu, the north lunar node, is calculated as the mean lunar node by the formula in Jean Meeus's "Astronomical Algorithms". Ketu, the south lunar node, is placed 180° opposite Rahu.

The lagna, the sidereal ascendant on the eastern horizon, is the tropical ascendant minus the true ayanamsa. Houses are whole signs from the lagna, so each 30° sign forms one house. Because whole-sign houses don't depend on quadrant cusps, there's no problem near the poles.

Nakshatras, padas and karakas

The 360° zodiac is divided into 27 nakshatras, which are lunar segments of 13°20′ each. Each nakshatra is divided into four padas, which are quarters of 3°20′ each. To find your karakas, the planetary significators, we rank the planets by their degree within the sign. Positions are compared to the second of arc, and planets tied to the second of arc share a role.

The planet at the highest degree in its sign is the atmakaraka, and the planet at the lowest degree is the darakaraka. You'll see the seven-planet scheme by default, with the eight-planet scheme shown alongside it. In the eight-planet scheme, Rahu is counted as 30° minus its degree within the sign.

Time zones and places

Cities and coordinates come from the GeoNames database. Historical time zone offsets and daylight saving rules come from the IANA time zone database built into your browser. If the clocks went back on your birth date and a time happened twice, the form asks which one applies. If the clocks moved forward and a time never happened, the form says so.

The birth-day scan

The site also scans the whole birth day, both for the slider and for charts without a birth time. It checks every 2 minutes and narrows each change of the lagna, the Moon's sign, the Moon's nakshatra, the atmakaraka or the darakaraka down to the second. A value that changes and changes back within 2 minutes could be missed.

Change times for the lagna, the Moon's sign and the Moon's nakshatra agree with Swiss Ephemeris within 20 seconds. Karaka change times usually agree within about 3 minutes. When two slow planets swap places, a tiny difference in position moves the time much more: in our check, by up to 48 minutes.

How we checked it

We checked the calculations against Swiss Ephemeris, a reference ephemeris library widely used in astrology software. The check covered 22,001 charts from 1900 to 2050, including places above the Arctic Circle. The mean ayanamsa differs by a constant 0.13″, the true ayanamsa we use by at most 0.27″, and Rahu by at most 0.12″. The Sun differs by at most 2.3″, the Moon by at most 12.7″ and the other planets by at most 20.1″.

Sign, nakshatra, and pada assignments differed only when a point sat within 30″ of a boundary. Karakas differed in 0.1% of charts, each time when two planets were within 30″ of each other in degree. The tables below give details for each check.

The numbers on this site

The statistics cited across this site come from a test sample of 4,000 random moments from 1950 to 2010. It's a test sample of moments in time, not a statement about all people. Across those 4,000 moments, the Vedic Sun sign differed from the Western one on 79.0%, and the Moon sign differed on 78.4%. The seven- and eight-planet schemes gave a different atmakaraka on 12.8% and a different darakaraka on 12.0%. One of the two differed on 24.9% of the moments.

The day statistics in that sample use the UTC day of each random moment. Within the day of the moment, the atmakaraka changed on 66.0% of the dates and the darakaraka on 64.9%. Over that same UTC day, the Moon sign changed on 43.3% of the dates and the Moon nakshatra on 95.9%.

Questions