Prarabdha karma are the part of sanchita karma, a collection of past karmas, which are ready to be experienced through the present body (incarnation).[1]
According to Swami Sivananda: "Prarabdha is that portion of the past karma which is responsible for the present body. That portion of the sanchita karma which influences human life in the present incarnation is called prarabdha. It is ripe for reaping. It can be avoided or changed by performing the right Karma to nullify the effects of Prarabdh Karmas. In normal way it is only exhausted by being experienced. You pay your past debts. Prarabdha karma is that which has begun and is actually bearing fruit. It is selected out of the mass of the sanchita karma."[2]
Each lifetime, a certain portion of the sanchita karma, most suited for spiritual evolution at the time, is chosen to be worked out during the course of the lifetime. Subsequently, this Prarabdha Karma creates circumstances that we are destined to experience in our present lifetime. They also place certain limitations via our physical family, body, or life circumstances into which we are born, as charted in our birth chart or horoscope, collectively known as fate or destiny (determinism).[3]