MUMBAI, Aug. 27 -- HDFC Bank earned INR 19,060 crore in net profit in the first quarter of FY27. The number beat no one. What the result actually showed was a lender with 15.4% loan growth, a 7% rise in net interest income, and a net interest margin that slipped to 3.26%, its lowest on record. The margin is where the story lives.

The Nifty Financial Services Index closed at 26,013 on August 19, down 0.36% on the day and essentially flat for the month. Against the Nifty 50's 12.4% year-to-date gain, the financial services index has delivered roughly 8% over the same period. The underperformance is not a story about weak fundamentals. It is a story about what the rate-cut cycle does to lenders on the way down.

The mechanics are straightfo...