I am just curious to know how does Karma work for a person who has converted to Hinduism.
If we consider Karma as a bank account; how is Karma accounted for a converted individual? Is it the Karma after conversion or the Karma since birth?
Karma is what you had done and what you are doing in your life time. So Karma will be there from the very next moment of your birth. There is nothing to do with Hindu, Muslim or Christian.
The Karmaphalam, Fruit(Reward) for your Karma will be awarded to you in your life time, may be in your next life too. Whether you are or were a Hindu or Muslim or Christian won't be considered in this.
Karma is the work or action or activity.
Karma never binds you, only your intentions, wishes, willingness from that Karma's gains binds you. Your own wishes, gain desires and your own thoughts bind you with good or bad fruit of Karma.
Every soul who is in body performs activity (Karma), so Karma theory is beyond religion.
Karma theory is exactly like Newton's third Law.
It is like resultant force of your applied force.
One who is soul in body this law applies to him. Being hindu, muslim, sikh or isai has nothing to do with anything. Even this law is applicable to animals. Every living being comes under this Karma theory.
Just make sure you perform your activities as Vairagi (Desire less Person), and with duty, rise above fruits, Moha attraction and just do it as it is GOD's will, that Karma will never bind you according to Karma Yoga of Shrimad Bhagwat Geeta. But this applies to all souls nevertheless of they are from any religion, converted to some or not.
Is Karma accounted?
Yes but not from birth, from your "first birth on Mrutyu Loka", your Karma is accounted, noted and you can only be freed by attaining Moksha. Hindu scriptures states that Chitragupta notes every activity of all souls on Mrityuloka, when a person dies his judgments are done on behalf of his activities only. He may face his fruits in next lives also. But judgement is always full of justice.
Almost all (may be 75%) religions have theory of judgement, paradise and hell. Almost all of them have concept of Dharmaraj or Yama.
Hinduism is not a sectarian religion in which certain things depend on your conversion to or from. It is called the Eternal Religion and rightly so. Law of karma affects us all regardless of what earthly beliefs and identities we have. Yes law of karma acts upon each and every individual and it is free of conversion. In fact it is not from birth but even before that, from previous lifetimes.