Vimshottari years of each graha
Each graha has a fixed number of years in the Vimshottari dasha: 120 years in total for the nine grahas. Each dasha is a period of one graha as the ruling lord.
What it is
Ketu 7, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19 and Mercury 17 years. The order is Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, and it repeats.
How it is worked out or read
The dasha years are fixed in the Vimshottari table and do not depend on the chart. The length of a year in the calculation is 365.25 days, which the dasha tool uses.
Where it appears on this site
The sequence and years are shown on the dasha tool. The Vimshottari article explains how the cycle starts.
The years and their sum
Each graha has a fixed length in the Vimshottari table: Ketu seven years, Venus twenty, the Sun six, the Moon ten, Mars seven, Rahu eighteen, Jupiter sixteen, Saturn nineteen and Mercury seventeen. Together they sum to 120 years. The table is fixed and does not depend on the chart, so these lengths can be memorised and used for any birth. The reader who knows them can estimate the length of any period without a calculator.
The order in which the grahas appear is also fixed: Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn and Mercury. The sequence then repeats. Because the years and the order together define the whole system, learning both gives a reader the core of the Vimshottari method.
Why these particular numbers
The lengths are part of the classical Vimshottari table and are not derived from astronomical periods in a simple way. Their traditional rationale is given in the texts, and the reader can study that rationale in the sources. This site uses the table as given and does not claim that the numbers correspond to any physical cycle.
Some readers notice that Venus and Saturn have the longest periods among the seven visible grahas, while Ketu and the Sun have the shortest. The pattern is a feature of the table, and it shapes how long a person spends under each theme during a life.
Estimating a period quickly
A quick way to estimate a period is to take the lord's years, multiply by 365 days to get an approximate length, and check the result against the tool. The exact length uses 365.25 days, so the estimate will be slightly short for long periods. The estimate is useful for planning, while the tool gives the exact dates.
Using the years in mental arithmetic
Learning the nine lengths well makes many dasha questions answerable in the head. Venus twenty and Saturn nineteen are the longest, so a period under them lasts a long time. Ketu seven and Mars seven are the shortest together with the Sun six. Knowing that Rahu eighteen and Jupiter sixteen are both long, and that Mercury seventeen sits between, gives a quick sense of the cycle's shape.
Mental arithmetic is also useful for checking a balance. If a Moon has crossed half its nakshatra with Venus as lord, the balance is near ten years, and a reader can see at once whether a tool's result is reasonable.