The word Kalathra means spouse. Among the planets, Venus is the kalathra karaka (planet indicating wife). Among the 12 houses, 7th house is the kalthra sthana(house indicating spouse). Any malefic planet in 7th house creates kalathra dosha. Also, kalathra dosha is created if the 7th lord and venus is afflicted in the birth chart. Kalathra dosha delays the marriage and it is very hard to find a suitable partner for marriage. Even after the marriage, they lack good understanding and live a separated life. They also lack conjugal bliss which ultimately ends up in divorce. In some cases, the spouse suffers due to health problems and even death may occur in severe cases.
Similarly, 8th house is called as mangalya sthana(house indicating marital tie). Malefic planets in 8th house create Mangalya dosham. Planet Jupiter is called as the mangalya karaka (planet indicating marital tie). If the 8th lord, Jupiter and 8th house is afflicted, then the person faces trouble in marital life due to mangalya dosham. Mangalya dosha will spoil the marriage life either by separating husband and wife by sending someone away from home or else by divorce or by giving death to the husband.
Exceptions on Kalathra dosha and Mangalya dosha:
If Jupiter aspects the 7th house or 8th house, then the dosha get cancelled.
If the lord of the 7th or 8th house is strongly placed, then the dosha doesn't harm much
If the planet creating dosha is placed on its own house or exaltation house, then there is no dosha.
There are several planetary combinations that cancel the kalathra dosha and mangalya dosha which are beyond the scope of this page. It is always suggested to leave the calculation and confirmation part to an experienced astrologer. The only point that can be spoken here positively is that the Kalathra dosha or mangalya dosha do not affect the native if they marry a person who has similar type of dosha in their birth chart. The Malefic effects of Kalthra dosha and Mangalya dosha gets reduced to a greater extent in case of Inter-caste Marriages and Love Marriages. In case if a proper match could not be made, then they should at least perform suitable remedies and nullify the malefic effects of the planet to make a peaceful marital lif
