Rooted in Truth
How we calculate
Every chart on this site comes from real astronomy and named classical sources. This page shows both, including where we fall short.
Where the positions come from
Planetary positions are computed from the same modern astronomical theories professional software uses, and then checked against NASA's JPL Horizons — the reference the world's space agencies use for where things actually are. We test twelve moments spread from 1912 to 2039. Every body lands within ten arcseconds of the reference, which is about a three-hundredth of a degree.
| Graha | Largest error |
|---|---|
| Jupiter | 9.8″ |
| Venus | 9.4″ |
| Saturn | 8.1″ |
| Moon | 7.5″ |
| Mercury | 4″ |
| Mars | 3.6″ |
| Sun | 2″ |
An arcsecond is 1/3600th of a degree. For scale, a nakshatra pada spans 12,000 arcseconds — so these figures are well inside the smallest division a reading normally uses. This is checked automatically every time the site is built.
The choices behind the numbers
Sidereal zodiac, Lahiri ayanamsa
We use the sidereal zodiac, measured against the fixed stars, as Vedic astrology does — not the tropical zodiac used in Western astrology. The gap between the two is called the ayanamsa, and it grows by about 50 arcseconds a year as the Earth wobbles. We use the Lahiri (Chitrapaksha) ayanamsa: the value fixed by the Calendar Reform Committee under Meghnad Saha in 1955, and published every year in the Rashtriya Panchang by the Positional Astronomy Centre of the India Meteorological Department, Kolkata. It is the standard used by the Government of India and by most Indian panchangs.
Time zone from your birth place and date
We do not ask you to know your own UTC offset. You tell us where you were born and when, and we look up what the clocks actually read there on that date. This matters more than it sounds: the rising sign moves a full degree every four minutes, so an hour wrong is half a sign and often a different Lagna altogether. Kolkata ran on UTC+6:30 during the Second World War, and on +5:21 before 1906. London was an hour ahead of Greenwich right through the winters of 1968 to 1971. No dropdown can express that; a date can.
Whole-sign houses
Each house is one whole sign, starting from the sign of the Lagna. This is the oldest and most widely used system in Indian astrology and the one the North Indian chart assumes. Other systems divide the houses unequally and will place a planet near a boundary differently.
Rahu and Ketu: the mean node
We use the mean lunar node rather than the true node. The true node wobbles about a degree and a half either side of the mean one. Indian panchangs and mainstream Vedic software use the mean node, so we do too — this is a difference of convention between schools, not a matter of one being correct.
Navamsa (D9)
Each sign divides into nine parts of 3°20', and where those parts fall makes a second chart. Classical practice reads the rashi chart as what is promised and the navamsa as whether it holds — and for anything about marriage the navamsa is the primary chart, not a supplement. The same 3°20' grid also defines the nakshatra padas, which is why the two are traditionally read together.
Vimshottari Dasha
The 120-year cycle of planetary periods, worked out from the Moon's exact position within its nakshatra at birth. We measure its years as 365.25 days, which is what modern Vedic software does. Some classical traditions use a 360-day year instead, which shifts long-range dates by a few months — again a genuine difference of school rather than an error on either side.
The classical sources
The calculations above are astronomy. What they mean is astrology, and that comes from a written tradition. These are the texts the interpretations on this site rest on.
Brihat Parashara Hora Shastra
The foundational text of the tradition. Houses, sign lords, karakas, the divisional charts, and the Vimshottari dasha system all come from here.
Brihat Jataka — Varahamihira, 6th century
The classic compact treatment of natal astrology. B. Suryanarain Rao's English translation of 1905 is in the public domain.
Phaladeepika — Mantreswara
One of the most-used practical handbooks, especially on house results and planetary yogas.
Saravali — Kalyana Varma
An extensive early compendium on planetary placements sign by sign and house by house.
Jataka Parijata — Vaidyanatha Dikshita
A widely-cited later synthesis, and one of the sources for the regional rules around Mangal Dosha.
Uttara Kalamrita — Kalidasa
The standard reference for karakas: what each graha signifies before any chart is drawn.
Where we fall short, said plainly
A page claiming accuracy owes you its limits too. These are ours.
- Mangal Dosha is not in the Brihat Parashara Hora Shastra. It comes from later regional practice, the rules differ between regions, and the cancellation conditions differ even more. We show the Moon-chart version and say so.
- Schools disagree about the ayanamsa itself by up to about a degree. We follow Lahiri because it is the Indian government standard, but a reading elsewhere using a different ayanamsa may legitimately place a planet in the neighbouring sign.
- The rising sign depends on an accurate birth time. If your recorded time is rounded to the nearest hour, treat the Lagna and everything counted from it as approximate.
- We calculate for latitudes up to 66 degrees. Beyond the polar circles the rising point of the ecliptic stops being well defined, and we would rather decline than print something confident and meaningless.
- Our free tools are a starting point, not a reading. They apply general rules; they cannot weigh one factor against another the way a person reading your whole chart does.
Have a question about any of this?
If something here does not match a chart you have been given elsewhere, tell us the difference and we will explain where it comes from.
Ask us