I am an Indian guy. More than 20 years back there was a fixed deposit of an amount of 20,000 Rupees on my name, after some period that amount was drawn it was more than double amount and utilized on my education and other aspects. After my maturity I refused to use it, my elders advised to use it for now, you donate it later, first make you career. That was done, and now I want to take out the excess amount which I have got with original deposit. My question is do I have to calculate the currency rate of that time and this time or no need, just the same amount to needy, and get rid of that amount of interest.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Depositing money in usurious banks is forbidden since they use it in their forbidden transactions. So, a Muslim should withdraw his deposited amounts from such banks as soon as possible. And the interest gained on the amounts should be given away for the public interest of the Muslims. This is forbidden money and can not be owned rather it should be spent on needy, poor and the like people.

Therefore, you did well by withdrawing your money but you made a mistake by using and keeping that money with you. You were obliged to spend it on the poor immediately.

Now you have to spend all the money which exceeded your original amount i.e. 20,000 Rupees.

You have to spend only the amount which exceeds your original amount regardless of the depreciation in the value of the currency.

Allaah Says (which means): {But if you repent, you may have your principal-[thus] you do no wrong, nor are you wronged.}[Quran 2:279].

So, you may only keep the capital amount, and anything that exceeds it is not your money.

Allaah Knows best.