Kal Sarpa Yoga is formed when the seven physical planets are hemmed between  Rahu and Ketu. For example, if Rahu is in Aries and Ketu in Libra, and the rest of the planets are located in signs Scorpio to Pisces, Kal Sarpa Yoga is formed.

The popular opinion in astrology about KSY is that it is very negative in nature, is harmful and it stops all progress in life. But, the fact is that KSY is effective only when the other planets and yogas are giving negative results too. It actually increases the negativity of other planetary combinations and is not a direct cause of any ill effects. Moreover, only the Rahu and the Ketu dashas are negative while other planets may show good or bad results depending on their placement in the horoscope.