Dashas
Dashas are a system of planetary periods, the main predictive tool of Jyotish. Instead of transits, as in Western astrology, life here is divided into long stretches, each ruled by its own planet.
If the time is unknown, tick the box: the Moon will be calculated for noon and the period boundaries will be approximate. Latitude, longitude and UTC offset are needed only if your city is not on the list; north latitude and east longitude are positive.
How It Works
The most widespread system is the Vimshottari dasha, designed around a 120-year span. The nine planets receive periods of fixed length:
| Planet | Period Length |
|---|---|
| Ketu | 7 years |
| Venus | 20 years |
| Sun | 6 years |
| Moon | 10 years |
| Mars | 7 years |
| Rahu | 18 years |
| Jupiter | 16 years |
| Saturn | 19 years |
| Mercury | 17 years |
That adds up to 120 years. The order is fixed and never changes.
Which planet life begins with is determined by the Moon's nakshatra at birth: its ruler gives the first period, and not in full but only the remainder, proportional to how much of the nakshatra the Moon has already traveled.
Sub-periods
Each maha dasha is divided into antar dashas (sub-periods) in the same planetary order and in proportion to their lengths, and those in turn into pratyantar dashas. Astrologers usually work with two or three levels of nesting.
Example: the 19-year Saturn period contains a Venus sub-period of about 3 years and 2 months, which has its own sub-sub-periods.
Interpretation is based on the combination: how the period planet is placed in the chart, how it relates to the sub-period planet, and which houses they rule.
How the calculator works
The Moon's position is calculated with Jean Meeus's lunar theory in the sidereal zodiac with the Lahiri ayanamsa. From it the calculator finds the nakshatra, its ruler and the share the Moon has already covered; the first Mahadasha gets the remainder of its term, and the rest run in full. Sub-periods are divided proportionally: Antardasha length = Mahadasha × the sub-period's years / 120.
A year is 365.25 days, as in most software. The birth time matters: the Moon moves about half a degree per hour, and a one-hour error shifts all period boundaries by 3–10 months.
Why the Design Is Interesting
Dashas are a purely calendrical construct: everything is derived from a single value (the Moon's position at birth) and then runs automatically, without regard to the planets' actual motion.
This makes the system fully deterministic and, in principle, testable: the durations are fixed and the period boundaries are calculated exactly. If a link to events existed, it could be detected statistically.
No such confirmation exists. There is, however, a clear reason why the system seems to work: 120 years are split into nine periods with 81 sub-periods inside, and for any turning point in life there will always be some period boundary nearby.
Other Dasha Systems
Besides Vimshottari, there are Ashtottari (108 years), Yogini (36 years), Kala Chakra, and several dozen others. They produce different divisions of the same life.
Astrologers choose a system based on their school and the situation. From a testing standpoint this is a weak spot: having many mutually exclusive schemes, each considered valid, shows that there is no selection criterion.