How a Sri Lankan Bank Makes Money

Banks dominate the Colombo Stock Exchange, and yet many investors buy bank shares without really knowing how a bank earns its profit. Using a major private bank such as Commercial Bank as our example, let's open the engine and look inside. Once you see how the money is made, you can judge any bank far more clearly. This is a framework, not a recommendation.

The engine: net interest margin

A bank pays you a little interest on your savings, then lends that money to borrowers at a higher rate. The spread between the two is the net interest margin (NIM), the heart of banking profit. The cheaper a bank's funding and the better its lending, the wider the margin.

The secret weapon here is low-cost deposits, current and savings accounts (often called CASA) that pay little or no interest. A bank with lots of these has cheaper raw material than a rival relying on expensive fixed deposits, and that funding advantage is a genuine moat.

Beyond interest: fee income

Good banks earn more than the spread. Fee and commission income, from cards, trade finance, remittances, and transaction services, adds profit without tying up as much capital. A healthy mix of fee income makes a bank less dependent on interest rates alone.

The deposit franchise as a moat

Why can't anyone start a bank and compete? Because a large, loyal deposit base takes decades and deep trust to build. Combine that with a wide branch and digital network and real scale, and you have an advantage newcomers struggle to match. This is why the big, established banks tend to stay big.

A bank's most valuable asset is not its loans; it is the trust that keeps millions of depositors leaving their money there cheaply. Lose that trust and the whole model wobbles.

The big risk: credit and the economy

Here is where banks get dangerous. When a bank lends, some borrowers will not repay. In good times this is manageable; in a downturn, bad loans (non-performing loans, or NPLs) pile up, and the bank must set aside provisions that eat into profit. Because banks are so leveraged and so tied to the wider economy, they amplify the cycle, thriving in booms and suffering in busts. Sri Lanka's recent crisis, including strain from government debt exposure, showed exactly how quickly bank fortunes can turn. To understand a bank, you must understand the economy around it.

Regulation, capital, and how to read a bank

Because a bank failure hurts everyone, banks are tightly regulated by the Central Bank and must hold enough capital to absorb losses. That safety cushion limits how aggressively they can chase profit, a healthy tension. When you assess a bank, look past the headline profit to a handful of tells: