Vimshottari is the timing system that makes a Jyotish chart move. Western practice reads a natal chart and then looks for transits to it; Jyotish reads the chart through whichever planet currently holds the clock.
Vimshottari dasha is the dominant time-lord system in Jyotish, dividing life into consecutive planetary periods that total 120 years: Venus 20 years, Saturn 19, Mercury 17, Rahu 18, Jupiter 16, Moon 10, Mars 7, Ketu 7 and Sun 6. The sequence never changes, but where a chart enters it does: the lord of the janma nakshatra, the mansion holding the Moon at birth, rules the first mahadasha, and the portion of that mansion the Moon has already crossed is subtracted from it. Each mahadasha subdivides into antardashas in the same order and proportion, and those into pratyantardashas. Astrolium computes 3 levels of the sequence and warns when a birth time sits near a boundary.
The period lengths
Nine lords, in this fixed order: Ketu 7 years, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19, Mercury 17. Added together they make 120 years, the nominal full life span the system assumes, and the name comes from that number.
Most people live through 4 to 6 mahadashas. Which ones, and in what order, depends entirely on where the Moon sat at birth, so two children born in the same hospital an hour apart can open life under different lords and follow entirely different sequences from then on.
The balance at birth
The starting point comes from the nakshatra holding the Moon. Each mansion spans 13 degrees 20 minutes and belongs to one of the nine lords. Measure how far the Moon has travelled into its mansion, express that as a fraction, and remove the same fraction from the lord's period. A Moon 40 percent through Pushya, ruled by Saturn, starts life with 60 percent of a Saturn mahadasha left, which is a little over 11 years of the full 19.
Because the Moon moves roughly 13 degrees a day, this calculation is sensitive to the recorded time. A chart near a mansion boundary can change its opening lord on a correction of a few minutes, which is why serious dasha work starts with an honest look at the birth record.
Sub-periods
Each mahadasha divides into 9 antardashas, sometimes called bhuktis, running in the same order and in proportion to their own period lengths. Inside a 16-year Jupiter mahadasha, the Jupiter antardasha comes first and runs about 2 years 2 months; the Venus antardasha inside it runs about 2 years 8 months, because Venus holds the largest share of the cycle.
The same proportional rule divides each antardasha into pratyantardashas, and lineages that want more resolution keep going. In practice, most reading stops at the third level. The first two describe the chapter, the third describes the season inside it, and beyond that the periods are short enough that transits are the better instrument.
How it is read
The dasha lord acts as a filter on the whole chart. Whatever that planet rules by house, wherever it sits, whatever dignity it holds and whatever aspects it receives comes forward for the length of its period. A well-placed 9th lord running its mahadasha tends to produce the 9th house story: teaching, travel, a change of philosophy. The same planet debilitated and afflicted produces the same themes under strain.
Two planets are read together: the mahadasha lord and the antardasha lord, with their mutual relationship, friendship, enmity or exchange, colouring the sub-period. Transits are then read against that frame rather than on their own, which is roughly the reverse of the Western default.
In Astrolium
The Jyotish timing module computes mahadasha, antardasha and pratyantardasha for a saved chart, shows the balance at birth, and flags fragility directly: it will tell you that a birth time a given number of minutes different would change the mahadasha lord. Dasha boundaries are stated in the birth-place civil calendar rather than passed off as UTC instants.
The free Vedic birth chart calculator returns the current mahadasha and antardasha with the full 120-year timeline. For the annual chart read inside the running period, use the Varshaphal calculator, and for the wider framework see the Vedic astrology guide.