Vimshottari dasha explained
Vimshottari dasha is the most used planetary period system in Jyotish: a 120-year cycle divided among the nine grahas, starting from the Moon's nakshatra at birth.
What it is
The nine lords follow the order Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, with years 7, 20, 6, 10, 7, 18, 16, 19 and 17. The cycle then repeats. The first dasha at birth is the lord of the Moon's nakshatra, and it is only partly run at birth.
How it is worked out or read
The lord of a nakshatra is its index modulo 9, read in the order above. The balance of the first dasha is its full years times the fraction of the nakshatra still to be crossed. Each mahadasha is then followed by antardashas, which are described in the mahadasha article.
Where it appears on this site
The dasha tool computes the full timeline. See dasha balance at birth for the first period.
Why the Vimshottari system is the usual choice
The Vimshottari system is the planetary period scheme most often used in Jyotish. Its 120-year cycle gives every graha a fixed length, and the sequence is simple enough to calculate by hand once the Moon's nakshatra is known. Most classical and modern practitioners who use dashas begin with it, which is why this site computes it and does not compute the other systems. A reader who wants to compare systems can see the differences in the article on dasha systems compared.
The system is also tied to the nakshatra structure. Because each nakshatra has a lord in the Vimshottari order, the nine lords repeat three times in the 27 nakshatras. This means that a birth in any given nakshatra starts the cycle at a predictable point, and the reader can check the starting lord against the nakshatra table without any further calculation.
The arithmetic of the first period
Suppose the Moon is halfway through its nakshatra at birth. The lord of that nakshatra rules the first period, and only half of its full years remain. If the lord is Venus, with twenty years, the balance is ten years. If it is Ketu, with seven years, the balance is three and a half years. The tool gives this balance and the start and end dates of the first period, so the reader does not need to compute it by hand, but can check it by hand if needed.
After the first period ends, the sequence continues in the Vimshottari order, with each full period lasting its full years. The reader can therefore follow the timeline from birth to any later date, and the timeline is stable because it does not depend on the chart's other features.
What the periods do and do not show
A dasha period shows when one graha's rule is active in a chart. It does not show what will happen in that period, and no classical text claims that dasha dates alone decide events. Readers who use dashas usually combine them with the natal chart, with the transits of the slow grahas and with the strengths of the lords. The site presents the timeline as a timing calculation, and any reading of the periods is shown as a traditional interpretation that the reader can weigh.
It is wise to treat the timeline as a map of when a theme is active, rather than as a forecast. A reader planning around a period should check the dates against a second source if the timing matters, and should not rely on one period alone.