The economics of HDFC Bank come down to a simple spread — borrow cheap, lend carefully, collect fees on everything in between — but the execution is anything but simple. Start with deposits. The bank gathers roughly $180 billion in customer deposits, and the mix matters enormously. Current accounts pay zero interest. Savings accounts pay 3-4%. Together they form the CASA ratio — the percentage of deposits that cost almost nothing. Before the 2023 merger, HDFC Bank's CASA ratio sat comfortably above 45%. Post-merger, it dropped closer to 38% because HDFC Ltd's mortgage book came with wholesale funding, not sticky retail deposits. That single number — CASA ratio — explains most of management's strategic anxiety right now. On the lending side, the bank runs three engines simultaneously. Retail loans (home loans, personal loans, auto finance, credit cards) generate the highest margins and the most predictable cash flows. Commercial banking serves SMEs and mid-corporates with working capital and trade finance — higher yields but more credit risk. Wholesale banking handles large corporates at razor-thin spreads but enormous volumes. The credit card business deserves separate attention. With 20 million+ cards in force, HDFC Bank is India's largest issuer. Each card generates revenue four ways: interchange fees from merchants (1.5-2% of every swipe), annual fees, interest on revolving balances (36-42% APR in India), and co-brand partnership fees from companies like Amazon, Flipkart, and Tata. Cards alone probably contribute $1.5-2 billion in annual revenue. Then there's the fee machine: wealth management distribution (mutual funds, insurance), trade finance processing, cash management for corporates, foreign exchange, and payment gateway services. Fee income runs at roughly 30% of total revenue — not as high as a pure investment bank, but critical because it doesn't consume capital. The merger math is straightforward in theory: HDFC Ltd brought $100+ billion in mortgage assets and millions of borrower relationships. The bank's job is to convert those mortgage-only customers into full banking relationships — savings account, salary credit, cards, insurance, investments. Each conversion reduces funding costs (because the customer's salary now sits in a low-interest savings account) while increasing fee income. Management estimates each converted customer can yield 3-5 additional product relationships. FY2025 numbers: $25.6 billion total income, approximately $7.9 billion net profit, return on assets around 1.9%, return on equity near 16%. Those are strong numbers for a bank this size, but they're compressed from pre-merger levels because the mortgage book earns thinner spreads than the legacy retail portfolio.