Net interest margin (NIM) is a measure of the difference between the interest income earned by a bank or other financial institution and the interest it pays out to its lenders (for example, depositors), relative to the amount of their assets that earn interest. It is similar to the gross margin or gross profit margin of non-banking finance companies.
NIM is usually expressed as a percentage of what the financial institution earns on loans in a time period and other assets minus the interest paid on borrowed funds divided by the average amount of the assets on which it earned income in that time period. In other words, it’s what net interest income a lender earns in percentage terms on the average interest-earning assets in a specified period.
For example, if a bank’s average interest-earning assets, which may include loans and investment securities, stood at Rs 10,000 in a year and it earned an interest income of Rs 600 and paid interest expense of Rs 300, the NIM would be (600 – 300) / 10,000 = 3 per cent.
Source: Economic Times