Let's take a look at wells fargo. https://www.marketwatch.com/investing/stock/wfc/financials https://www.marketwatch.com/investing/stock/wfc/financials Intere

Let's take a look at wells fargo. https://www.marketwatch.com/investing/stock/wfc/financials https://www.marketwatch.com/investing/stock/wfc/financials Interest income: 53.66B Interest expense: 5.91B Net interest: 47.75B Net income: 21.94B so already, we're working off of closer to 40% net margin. Now let's look at what actually causes the difference between those numbers: >10.08B in taxes Pretax is 32.12B, so there's about 15B left to explain This turns out, roughly, to be the difference between Non-Interest Income and Non-Interest Expense - in other words, stuff that isn't really related to regular banking stuff. I'm not going to repeat this analysis for another 1000 banks, but it seems like, at best, you might double that number if you decide that some of these expenses aren't needed.