Credit card companies make 3/4 of their revenue from interest. From Capital One's 10k, Net Interest Income vs. Total Net Revenue:

  2023: 79.5%
  2024: 79.8%
  2025: 80.2%

I don't really know my way around corporate filings, but...is that just for credit cards?

Capital One also is supposedly huge on car loans; I'd imagine the interest from those would comprise a big chunk of that revenue.