Net interest income

Interest earned on loans and investments minus interest paid on deposits and borrowings. It is a bank's core revenue line, before fees and before any credit losses.

Say a bank earns ₹4,200 crore of interest income and pays ₹2,450 crore of interest expense. Subtract one from the other and it reports ₹1,750 crore of net interest income.

Growth in the line comes from two places and they behave very differently. More loans at the same spread is volume growth. It repeats, and it consumes capital. A wider spread on the same book is margin expansion. That's usually a function of the rate cycle, and it reverses.

So before you extrapolate the growth, decompose it.

Interest earned, less interest paid. That's the business.

Fee income sits alongside and behaves quite differently. Processing fees and distribution commissions on insurance and mutual funds arrive without consuming capital. So do card interchange and transaction charges, which makes all of them the highest-quality revenue a bank earns. A bank whose fee income grows faster than its loan book is improving the shape of its earnings, because it's earning more without needing more equity behind it. Banks disclose fee income by component, and the split matters. Fees tied to lending volumes disappear when lending slows. Transaction and payment fees don't.