A young person has never had an income before, so she was always dependent on her parents. Now she is working and will be earning monthly. The parents have never taken out khums before and do not have an intention to, as they do not believe in its need or requirement. For the youth who understands khums as being wajib, how can she start to calculate her own khums owed, to at least make her personal belongings tahir/pure? The youth has a car, clothing and personal items that were all given by the parents, or through gifted money. Should she begin by listing all her currently owned items and their value, then calculating one-fifth of that? And what about items in the past that have already been donated or thrown away, like old clothing or books? How can the youth try to make-up past due khums to the best of her ability?

She does not need to pay khoms for the items she bought and used in the same year, except if she used them once, and decided that she will not use them again any more in the same year of purchase.
She needs to pay the khoms of such items, if they have market value, as used stuff.
If she do not remember that she went across such situation, she does not need to bother.
Now, since she started work, the day she started to work becomes her khoms day. Hence, she needs to see her saving (balance) throughout the year, on the same day annually, and pay its khoms.