DASA BHUKTI ANTARA:
Astrologers generally adopt  dasa system for judging the nature of events for the native or to time events. Every individual has to pass through different periods of good and bad days. The astrologer while analyzing the horoscope basically dependents on dasa/bhukti/antara periods arrived from the birth chart [ or horary] This helps in knowing mot only past events of the native. but also pin pointing future events Say in order to ascertain the best period or exact period when a native will get job or get parried etc, the relevant favorable dasa bhukti antara period are marked by the astrologer for prediction after studying the chart in detail.

Total life span of a native was fixed at 120 years. There is no clear clue why total dasa period adopted as 120 years. Astrologers in the pastmight have taken the optimum longevity of a native  in those periods as basis. Even know a percentage of population cross century..

Each  Star lord is allotted fixed no of Solar years.  Total solar years  ie 120 years  is  distributed among 9 stars  as under.

KETU—7YEARS, VENUS—20 YEARS,SUN---7 YEARS, MOON---10 YEARS
MARS---7 YEARS,RAHU---18 YEARS, JUPITER---16 YEARS SATURN—19 YEARS, MERCURY—17 YEARS

The period may also be called as total DASA   period of each planet.

Dasa of a native starts right from his birth. It is calculated based on Moon position at the time of birth The exact longitude of Moon and the constellation in which it is deposited is noted along with the star lord or Constellation lord.

For example 

In a native chart Moon is posted in Taurus sign @17.d 34min. we can say it is in moon star Rohini. [ 0-10 deg belong to  sun star krithika .in Taurus ]  and it has already traveled 7d.34m

Each star longitude is 13d.20m or 800 minutes. Here moon has traversed 454 minutes and balance moon dasa   will be 346 minutes in the star Rohini  If one has to calculate balance das at birth   it will be 346/800 x10 =  4.325 years or 4 years.3m.27d. [ minutes traversed  in the star dived by total minutes for the star  multiplayer by dasa period of the star in question]

here readers may ref ready beckoner books available in the market  one can   also  adopt simple formula  without reference  to books dasa period  for all planets

If we use the above table for above example
For Moon dasa longitude 13.20 –7.34 = 5-46 deg   balance @ birth
5 x 0.9.0 y   =     3y09m.00d
46  x  0.05   =     0y.06m.27d 
                           --------------          
                           4y03m.27
After initial dasa at bitrth, next dasa will follow in  a fixed order of dasa periods. So in this case after moon it will be mars dasa ,next rahu ,Jupiter, sat, mer, ketu ,venu, and last  sun dasa to complete the chain  or cycle of dasa periods.

Bhukti:
Dasa of each planet is sub divided into Bhukti  and further into antara, sookshma.
These sub divisions are available in the astrology   books.
Nemji garu we may consider giving the table of dasa bukti antara from software  
However it can be also  be arrived at by simple formulas Bhukti
Running Dasa period  x dasa period of the required bhukti
The result will be in months represented by first two digits and  the third digit should be multiplied by 3  [3 is constant]  to  get days.

For example  let us take venus dasa and various bhukti Venus dasa is of 20 years So venus bhukthi will be 20 x 20 = 400. {40 months or 2years and 6 months. Third digit here is zero so nil days }  2years 6 months.

Next .

Antara:
Now to calculate antara
Formula is running  dasa period   x bhukti x  antar dasa /40[40 constant]
Result will be in days
Ex   for ven dasa,venus bhkthi,venus antara ,  20x20x20  =8000/40 =200 days 0y.6m.20d
Sat dasa.venus bhukti and mars anttara
19x20x16 =2660 did by 40 = 66.5 days or 0y.2m.6d.12hours

Sookshma:
Now to calculate
Dasa x  bhukti x antara x sookshma  periods divided by 200  [200 constant ]
 result will be in hours.

Ven x vn ven ven  
20x20x20x20 /200 =1,60,000/200 =800 hurs or 1m3d