The basic idea
Vimshottari Dasha divides a cycle of 120 years among the nine grahas. Each planet takes charge for a fixed number of years, called its Mahadasha. During that time, the themes of that planet, the houses it rules and the house it occupies in your chart are said to come to the foreground.
The nine periods
The order never changes: Ketu 7 years, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19 and Mercury 17. Together these add up to 120.
Where your cycle starts
Your starting period depends on the Moon's nakshatra at birth. Each nakshatra belongs to one of the nine planets in a repeating sequence, so Ashwini, Magha and Mula belong to Ketu, Bharani, Purva Phalguni and Purva Ashadha to Venus, and so on through the list. If you were born with the Moon in a Venus nakshatra, you are born into a Venus Mahadasha.
You are rarely born at the start of a period. The calculator measures how far the Moon had travelled through its nakshatra and subtracts that share of the first Mahadasha, which gives the "balance" remaining at birth. This is why the first period in your timeline is usually shorter than its full length.
Sub-periods
Each Mahadasha is divided into nine Antardashas (sub-periods) in the same planetary order, starting with the main planet itself. The length of a sub-period is the Mahadasha length multiplied by the sub-lord's years and divided by 120. For example, Saturn's sub-period inside Jupiter's 16-year Mahadasha lasts 16 x 19 / 120, which is about two and a half years. Each Antardasha is divided again into Pratyantardashas using the same rule.
How to read a period
- Look at the house the dasha planet occupies, since that area becomes active.
- Look at the houses it rules, since those themes are also drawn in.
- Check its dignity and its relationship with the Lagna lord.
- Read the Antardasha lord the same way and note how the two planets relate.
- Remember the period shows timing, not a guaranteed event.
A note on accuracy
Different software uses slightly different year lengths, so exact start and end dates can differ by a few days between programs. This calculator uses a mean year of 365.2425 days. Because the starting point comes from the Moon, an inaccurate birth time can shift the whole timeline.
Jyotish is a traditional interpretive system rather than a science. Use this guide for learning and reflection, not as professional advice.
Related: How to read your Janam Kundali and the twelve houses.