All who know basics of Indian astrology knows that longevity of a chart of prime factor without which detailed analysis of the horoscope is of not much usefulness.
The prevalent methods of longevity determination are the following:-
(1) The method of 3 pairs of lagnalord and 8th lord, lagna and horalagna , and the pair of saturn and moon depending upon their placement in movable sign (longlife), fixed sign(shortlife) and dual sign(middle life).
(2) The strengthe of lagna lord, 8th lord and 10th lord on the basis of their natural strength, placement and association. Kendra placement, freedom from debilition , affliction. combustion and placement in boarder of signs (also called rasi sandhi)
(3) Strength of Lagna / Moon/ Sun,
strength of their rasi and navamsa lords
(4) The strength and placement of lagna/ 3rd/8th house
depending upon the planet occupying or aspecting them with rasi drishti
and the strength of lagna lord, 3rd lord and 8th lord
(5) The strength of lagna lord, 5th lord and 9th lord and their dispositors to see whether remedial measures will be successful to increase the longevity
(6) Another method is to note down the rasi placement of the 4 kendra (quadrant) lords of the navamsa chart along with their natural strength
(7) To check the placement of sub lord, starlord and sign lord of the ascendant or lagna in the rasi chart.
(8)Rule on Placement :
Placement in houses 2,7,12 and badhaka houses gives short life, in kendra houses and trikona housesand houses 3 and 8 give longlife and in remaining houses- gives medium life.
Additional Rules-
( 9) Affliction by nodes: where nodes owns trine houses and placed in kendra houses... affliction will be minimal giving to longlife as well as raja yoga.... as the planet would turn Yogakaraka for the chart.
(10)Papamadhya- whenever a planet or a house is sorrounded by malefics in 2nd and 12th signs/ houses from it.. the planet/house looses its vitality to give good result or long life
(11) Exception to papamadhya: Whenever the natural malefic planets forming Papamadhya yoga for a planet or a house...please check if these two natural malefics e.g. sun and mars for dhanu(sagitarius) or simha (leo) lagna or mesha(aries); are Yogakara planet. Then instead of reduction... there would be strengthening of the results giving long life.
(12) The Bottom Line : If your lagna , lagna lord and moon sign are influenced by the lords of trines or Jupiter, Venus or unafflicted mercury or you have sun or mars in the 9th , 10th or 11th houses, be sure of a reasonable longer life ( over 75 years of age).