This is from "A Textbook of Varshaphala " by Dr K S Charak.

The Mudda Dasha is a system which shows the planetary periods for one year from the exact time of a solar return chart (or Varshaphala) and is the equivalent of the Vimshottari Dasha periods for a natal chart, proportionally reduced from 120 years to one year or 360 days.

It is also based on the 's Nakshatra at the time of birth, and is calculated like this:

The first dasha is found by adding to the completed years of life, the 's Nakshatra at birth, subtract 2, then divide the total by 9.

Ignore the quotient, and the remainder is the Mudda dasha period operating at the start of the solar return year.

The balance of the dasha remaining depends on the 's longitude at the time of birth, in the Nakshatra.

As the Mudda Dashas only operate for a year instead of 120 years, the duration of each dasha in days is obtained by multiplying its Vimshottari year-period by 3, e.g = 6 x 3 = 18 days, = 10 x 3 = 30 days

There are aso sub-periods (Bhukti) which also follow the same proportions as the main periods (Maha dashas).