If Jupiter in 12th house, then The native will be poor, he will be interested in studies, will have few children, will be proficient in mathematics but will be of loose character. He will be a leader of goons or thieves and like to involve in battle of arguments.
If Jupiter is associated with a benefic or is in his own sign or sign of exaltation, the native will go to heaven after his death. If Jupiter is associated with a malefic the native will go to hell after his death. He will spend money on religious causes and will have sexual contacts with Brahmin and pregnant women.
The twelfth house is an evil house and Jupiter though a satwick planet loses all his good significations and qualities when he is posited in that house. By being in the 12th house, the significations of the good houses owned by Jupiter are also adversely affected. The 6th and 8th and 12th houses have been called evil houses but if the lord of these houses are posited in any of these houses, Vipareeta Raja yoga is caused conferring name, fame and wealth on the native.
Other Views
Brihat Jatak- The native will be a villain.
Phaldeepika- The native will be disliked by other people. The native will also be vulgar in his speech. He will be childless, will indulge in sinful deeds, will be lazy and one who serves others.
Saravali- The native will be lazy, without good speech and unfortunate and will have a feeling of bitterness towards others.
Chamatkar Chintamani- The native in spite of spending on good causes will not get any praise. He will be stupid and will incur loss of wealth. "