1)Before knowing effect of Jupiter in 12th house first we have to know about Jupiter and 12th house. So you may read this.
Twelve house- house of expenses
Lord of sky Jupiter
2)Jupiter is karak of our religious activity and it is placed in 12th house which is consider as one of Dussthan so native may be involving in criticizing religious activity. Native may insulting religion. But if Jupiter is own sign or excellent then native may be very religious.
3)Jupiter is karak of Children and it is placed in 12th house so native may have problem related to children. Native have may have trouble through his children or native do not got happiness through his child. If Jupiter is heavily afflicted then it may cause death of child or health problems to kids.
4)Jupiter is moral teacher and it is placed in 12th house so native may be involving in immoral activity. Native may doing wrongly deeds. Native don’t shows good behavior. Native may be used abusive language and do not expert in speech. Native may be fraud and cheater. But Native may improving own self as per as time is pass. If Jupiter is well placed then bad effect is reduced and good is improve
5)As Jupiter is karak of wealth and it is placed in 12th house so native have financial problems regarding money. Native may have mental stress for his money.Native may not able to deposit so much wealth.
6)Jupiter is karak of fortune and it is placed in 12th house so it may cause for expenses of Fortune means native may loss his opportunity to get fortune.
7)Jupiter in 12th house makes native sexual .Native may be highly sexual desires.
9)Jupiter in 12th house indicating native may be serve other.
10)Jupiter in 12th house aspects all other Moksh trikona if Jupiter is well placed then native may be extremely religious or spiritual personality other wise it may indicating native may inclination regarding Materialistically pleasure and comfort.
11)According to Bhavarth Ratnakar native may be fortunate regarding those house whose karak is placed in 12th house. So Jupiter is karak of wealth regarding 2nd house, child regarding 5th house, Profession(karam) regarding 10th house,Profit regarding 11th house.