FAQ: How accurate is Jyotish?
The question of how accurate Jyotish is has two parts: the accuracy of the calculations, and the accuracy of the interpretations. The two need separate answers.
What it is
The calculations of planetary positions, sunrise and the panchang can be checked against astronomy and published almanacs, and are accurate to a small fraction of a degree when the inputs are right. The interpretations are traditional, and they are not established by controlled tests.
How it is worked out or read
So an accurate calculation can still be followed by an interpretation that is not supported by evidence. The site reports the calculations and labels the interpretations as traditional.
Where it appears on this site
For the calculation side, see the panchang software article. For the interpretation side, see Jyotish and science.
Two different questions
The question of accuracy has two parts that are often confused. The first is whether the calculations are accurate: whether the positions of the planets, the Lagna, the tithi and the nakshatra are correct. The second is whether the interpretations are accurate: whether what the tradition says those positions mean actually describes a person's life. These are very different questions, and they have very different answers.
Calculation: very accurate
The calculations can be made extremely accurate. Modern astronomical models give planetary positions to a small fraction of a degree for any date in recorded history, and the panchang's times to within a minute or so, given correct inputs. The main sources of error are the inputs themselves, especially the birth time and time zone, and the choice of conventions such as the ayanamsa. On these matters, Jyotish software can be checked against astronomy and against published almanacs, and good software passes those checks.
Interpretation: a matter of tradition
Interpretation is different. The meanings given to signs, houses, yogas and dashas come from a long tradition of texts and practice, not from measurement. Scientific studies that have tested astrological claims under controlled conditions have generally not found effects beyond chance. Many people nonetheless find the tradition meaningful as a framework for reflection, as a cultural practice, or as a way of marking time and ritual. This site presents interpretations as traditional readings and does not claim that they are scientifically demonstrated.
Why readings feel accurate
Readings can feel accurate for reasons that have little to do with the chart. General statements apply to most people; people remember the hits and forget the misses; and a skilled reader picks up cues from conversation. Knowing these effects does not make the tradition worthless, but it is a good reason to be cautious about specific predictions and about decisions based on them.
A sensible stance
A balanced approach is to trust the calculations, after checking the inputs, and to treat the interpretations as a traditional language for thinking about life, not as forecasts. Major decisions about health, money, marriage and career are best made on practical grounds and with qualified advice, with the chart, if consulted at all, as one voice among many.