Answered by Ustadh Tabraze Azam
Question: Asalam aleikum respected Ulema,
I am in my twenties and currently have a good full time job. However I live with my parents and I pay for all my own expenses and have been doing so for a few years now.
I got my first full time position in the summer of 2012 and have been working since.
Growing up my father paid for my zakat yearly. Even recently he says he has.
I wanted to know how can I calculate and pay for every year’s zakat from the age of 20?
In addition, I do have assets (car, stocks), and I am owed a few thousand dollars.
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I pray that you are in the best of health and faith, insha’Allah.
 After you have been in possession of the zakatable minimum (nisab [see: e-nisab.com] for one lunar year, you would calculate your assets and deduct your immediate needs and debts from them. You would pay 2.5% on the resultant figure. [see the links below for details]
 If your father paid for your zakat on your behalf, and you knew he was paying for you, it would be valid. You do not need to repay the zakat due from those years.
And Allah alone gives success.
Checked & Approved by Faraz Rabbani