The Vimshottari Dasha System

Vimshottari (“120”) Dasha divides a full 120-year cycle among the nine grahas, each ruling a fixed span of years in a set order: Ketu → Venus → Sun → Moon → Mars → Rahu → Jupiter → Saturn → Mercury, which then repeats.

The starting point isn’t the birth date itself but the Moon’s exact nakshatra at birth. Each of the 27 nakshatras is ruled by one of the nine dasha lords (in the same fixed order, cycling every 9 nakshatras), and how far the Moon has already moved through that nakshatra at birth determines how much of the first Mahadasha has already “elapsed” before the person was even born — which is why the very first period in anyone’s dasha timeline is almost always a partial one.

Three levels are computed here. A Mahadasha is the major period, running anywhere from 6 to 20 years depending on the lord. Each Mahadasha is subdivided into nine Antardashas (sub-periods), in the same nine-lord order starting with the Mahadasha lord itself, each spanning a share of the Mahadasha proportional to that lord’s own years out of 120. Each Antardasha is further subdivided the same way into nine Pratyantardashas — the finest level this site tracks.

The self-similar proportional split is what makes the system tractable: a Jupiter Antardasha within a Saturn Mahadasha always gets the same fraction of that Mahadasha’s length, and a Mercury Pratyantardasha within that Antardasha always gets the same fraction again — regardless of which Mahadasha it's nested in.