Dur Yoga is considered as a malefic yoga in Vedic astrology. According to its prevalent definition; if in a horoscope, the lord of 10th house is placed in the 6th, 8th or 12th house, Dur Yoga is formed in such horoscope. Duryoga can trouble the native with problems related to profession, reputation, status, credibility and a number of other problems.
In real practice, Dur Yoga is not seen producing such results when only the aforementioned condition is met. Hence more conditions should be met in order for this yoga to be formed effectively in a horoscope. Looking at the first condition; the lord of the tenth house should be duly or partly malefic. Looking at the second condition; if the lord of tenth house is benefic; it should be weak or afflicted in the horoscope, in order for Duryoga to be formed in such horoscope.
Taking an example, suppose exalted Sun is placed in the sixth house of a horoscope in Aries. Scorpio rises in the ascendant. Sun rules the tenth house, it is benefic and it is strong. Hence Dur Yoga may not be formed in this case.
Taking another example, suppose Saturn is placed in the twelfth house of a horoscope in Pisces, in Cancer navamsha of Poorvabhadrapada nakshatra. Aries rises in the ascendant. Functional nature of Saturn is flexible in horoscopes with Aries ascendant. In the present case, Saturn is uncomfortable in Pisces as well as in Cancer navamsha of Poorvabhadrapada nakshatra. Hence it may turn much more malefic than benefic. Therefore, Dur Yoga may be formed in the horoscope. The concept of planets exhibiting tendencies to be benefic or malefic on the basis of the houses they rule in a horoscope has been explained in the chapter ‘Gemstones for House Lords’ of the book ‘Gemstones – Magic or Science (Revised Edition)’.
Once the formation of Dur Yoga is confirmed in a horoscope, the next factor to check is its strength. The strength of this yoga is calculated through the placements of lord of tenth house in various signs, nakshatras and navamshas; as well as through the influences of other benefic and malefic planets. The overall theme of horoscope also affects the strength of this Yoga.
Taking an example, suppose benefic Moon is placed in the sixth house of a horoscope in Pisces, in Scorpio navamsha of Uttarabhadrapada nakshatra. Moon is strong in Pisces but it does poorly in Scorpio navamsha of Uttarabhadrapada. Hence Duryoga may be formed in the horoscope but it may not be strong.
Taking another example, suppose debilitated Jupiter is placed in the eighth house of a horoscope in Capricorn, in Capricorn navamsha of Uttarashada nakshatra. Jupiter rules the tenth house and it is debilitated in its sign of placement as well as in navamsha. Hence strong Dur Yoga may be formed in this case. Such native may not achieve much success in profession; unless strong benefic planets interfere.
Looking at the running times; when Mahadashas (planetary periods) of benefic planets are in effect; malefic effects of Dur Yoga may reduce. When Mahadashas of malefic planets other than the lord of tenth house are in effect; malefic effects of this yoga may increase. When Mahadasha of the lord of the tenth house is in effect; the native may witness mixed results if such planet is benefic but weak; and he may witness malefic results if the planet forming Duryoga is significantly malefic and/or afflicted.