Question: My grandfather invested ₹50,000 in a fixed deposit 15 years ago. The FD was supposed to be for 5 years but he never renewed it. The bank says it is now in a "stale" account. Approximately how much should be the value today if the bank continued paying interest at the same rate of 8% per annum?
Answer: If the FD was automatically renewed on the same terms (many banks auto-renew FDs at prevailing rates, not the original rate), the calculation is complex. However, if we simply calculate compound interest on ₹50,000 at 8% for 15 years, it would be approximately ₹1,58,600 (₹50,000 × 1.08^15). In reality, the amount would be different because: 1) after the first 5 years, the renewal rates would have varied based on market rates at each renewal, and 2) banks often do not pay interest on "stale" or unclaimed deposits beyond certain periods, eventually transferring them to the DEA Fund after 10 years of no activity. The actual amount would need to be checked with the bank with proper documentation.

Supporting evidence:
title: rbi.org.in/FAQs.aspx
quote: The amounts credited to the DEA Fund are the credit balances in any deposit account maintained with banks (Commercial Banks, Co-operative Banks), which have not been operated upon for 10 years or more by the depositor, or any amount remaining unclaimed for 10 years or more, and includes the following: savings bank deposit accounts; fixed or term deposit accounts; Yes, customer/depositor can claim a refund of their unclaimed amounts from their banks
context: s Fund (DEA Fund) Scheme, 2014” was formulated by the Reserve Bank of India in exercise of the powers conferred upon it under Section 26A of the Banking Regulation (BR) Act, 1949 and all the powers enabling it in this behalf. Under the provisions of this Section, RBI has established the Depositor Education and Awareness Fund (Fund). The Scheme has come into effect from May 24, 2014, i.e., the date of notification of the Scheme in the Official Gazette of India.
2. Which are the amounts credited to DEA Fund? The amounts credited to the DEA Fund are the credit balances in any deposit account maintained with banks (Commercial Banks, Co-operative Banks), which have not been operated upon for 10 years or more by the depositor, or any amount remaining unclaimed for 10 years or more, and includes the following: savings bank deposit accounts; fixed or term deposit accounts; cumulative/recurring deposit accounts; current deposit accounts; other deposit accounts in any form or with any name; cash credit accounts; loan accounts after due appropriation by the banks; margin money against issue of Letter of Credit/Guarantee etc., or any security deposit; outstanding telegraphic transfers, mail transfers, demand drafts, pay orders, bankers cheques, sundry deposit accounts, vostro accounts, inter-bank clearing adjustments, unadjusted National Electronic Funds Transfer (NEFT) credit balances and other such transitory accounts, unreconciled credit balances on account of Automated Teller Machine (ATM) transactions, etc.; undrawn balance amounts remaining in any prepaid card issued by banks but not amounts outstanding against travellers cheques or other similar instruments, which have no maturity period; rupee proceeds of foreign currency deposits held by banks after conversion of foreign currency to rupees in accordance with extant foreign exchange regulations; and such other amounts as may be specified by the Reserve Bank from time to time.

3. When are the above specified amounts credited to the DEA Fund? The banks are required to transfer the credit balance in the accounts referred in Q No 2 above, to the DEA Fund on the last working day of the month subsequent to the month of completing 10 years of its continuous inoperative or unclaimed status. For example, the deposits becoming due to be transferred to DEA Fund (i.e., unclaimed for 10 years), in the month of April shall be transferred to the DEA Fund on the last working day in the month of May.