Net interest spread refers to the difference in borrowing and lending rates of financial institutions (such as banks) in nominal terms. It is considered analogous to the gross margin of non-financial companies.
Net interest spread is expressed as interest yield on earning assets (any asset, such as a loan, that generates interest income) minus interest rates paid on borrowed funds.
Net interest spread is similar to net interest margin; net interest spread expresses the nominal average difference between borrowing and lending rates, without compensating for the fact that the amount of earning assets and borrowed funds may be different.
For example, a bank has average loans to customers of $100, and earns gross interest income of $6. The interest yield is 6/100 = 6%. A bank takes deposits from customers and pays 1% to those customers. The bank lends its customers money at 6%. The bank’s net interest spread is 5%.
Successful Bank Asset/Liability Management: A Guide to the Future Beyond Gap, John W. Bitner, Robert A. Goddard, 1992, p. 185.