Loan, bank interest and tithes

Hello Rabbi,
We have 50,000 shekels that we wanted to put into a bank deposit bearing an interest rate of 4.9%.
Good friends found themselves in a difficult financial situation where they needed to take out a loan of 50,000. We wanted to lend them the money, and therefore the mitzvah of a lender. Our question is, is it possible to calculate the annual interest we were supposed to receive from the bank (about 2,500 NIS) and deduct it from our tithes?