There's a lot to like about Capital One (COF 0.79%). Just to name a couple of things, the bank has one of the highest net interest margins of a larger bank, and its merger with Discover Financial Services creates some interesting opportunities. However, there's one key number investors should also keep an eye on.

*Stock prices used were the morning prices of May 15, 2025. The video was published on May 19, 2025.