7 min · Goal: Calculate an antardasha length and explain why three levels are read together.
A mahadasha runs from 6 to 20 years. No single description covers two decades of a life, so each period subdivides into nine antardashas running in the same planetary order, beginning with the mahadasha lord itself.
So a Saturn mahadasha opens with Saturn–Saturn, then Saturn–Mercury, Saturn–Ketu, Saturn–Venus, and round the cycle.
Antardasha length = (mahadasha planet years × antardasha planet years) ÷ 120.
Within a 19-year Saturn mahadasha, the Venus antardasha runs 19 × 20 ÷ 120 = 3.17 years, a little over three years and two months. The Sun antardasha in the same mahadasha runs 19 × 6 ÷ 120 = 0.95 years, under a year.
The proportions are elegant: each antardasha occupies the same share of its mahadasha as that planet occupies of the whole 120-year cycle.
Each antardasha divides again into nine pratyantardashas by the same proportional method. These run weeks to months, and there are further levels below — sookshma and prana — which most practitioners regard as beyond what the method can reliably support.
Our view: three levels is the honest limit. Below that the periods are shorter than the precision of most birth times.
The mahadasha sets the decade’s theme. The antardasha sets what is active within it. The pratyantardasha narrows to months.
The combination matters more than either alone. A benefic antardasha inside a difficult mahadasha reads as relief within a demanding stretch; a difficult antardasha inside a favourable mahadasha reads as a setback within a broadly good period. The mahadasha is the weather, the antardasha the day.
The relationship between the two lords matters too. If they are natural friends, or both functional benefics for the Lagna, the period runs more smoothly than if they are enemies pulling different ways.
How long is the Jupiter antardasha within a Rahu mahadasha?