Vimśottari Mahadasha and Antardasha periods across a 120-year cycle.
Vimśottari Daśā divides a 120-year cycle into planetary periods (Mahadasha) and sub-periods (Antardasha), starting from the lord of the birth Nakshatra. It is the primary timing technique in Jyotish for when a planet's results are expected to unfold.
It is the most widely used timing system in Indian astrology: a 120-year cycle divided between the nine grahas — Ketu 7 years, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19 and Mercury 17.
By the Nakshatra the Moon occupied at birth. Each Nakshatra is ruled by one of the nine grahas, and how far the Moon had already travelled through it decides how much of that first Mahādaśā had already elapsed at birth.
The Mahādaśā is the major period ruled by one graha. Each Mahādaśā is subdivided into nine Antardaśās (sub-periods), one for each graha, in the same fixed order and proportional to their years.