How does a bank make money on a free checking account?
Alpha · claude-sonnet-5
Good — I can now confirm two of the manuscript's flagged open items, and I want to add a substantive critique the researcher's checklist doesn't quite surface.
What checks out cleanly
The community bank NIM figure is confirmed directly, not just in secondary quotes: "The community bank NIM increased to 3.81 percent, up 10 basis points from the prior quarter and up 19 basis points from the year-ago quarter." The industry figure is equally solid: "Industry net interest margin increased 1 basis point from the prior quarter to 3.32 percent." Both numbers in the manuscript stand without qualification — FDIC Quarterly Banking Profile, Q2 2026, https://www.fdic.gov/news/press-releases/2026/fdic-insured-institutions-reported-return-assets-137-percent-and-net.
On the Eighth Circuit timeline, the manuscript's sequencing is right but slightly underdescribed. Oral argument happened in May 2026, not some vague "2026": "The Eighth Circuit Court of Appeals heard oral arguments this week in Corner Post v. Board of Governors, a lawsuit on the Fed's debit interchange cap," dated May 15, 2026, and the dispute centers on a specific technical point — "the case hinges heavily on the definition of…
Beta · gpt-6-sol
Alpha is right that the premise stands, but I found a source-level error in the opening example that matters more than a framing caveat.
The FDIC labels a column “Treasury Yield,” but its note says that for checking and other deposits without a maturity, the number in that column is the effective federal funds rate—not a Treasury-bill yield. The manuscript therefore cannot say its roughly 3.6% Treasury-bill comparison comes from the checking row of the FDIC table. Its arithmetic is fine—$5,000 × 0.07% = $3.50 and $5,000 × 3.6% = $180—but the latter is an *illustration using an assumed yield*, not evidence that this bank earns $180 on this account. It should use a separately sourced bill yield if it wants to retain the Treasury example. Nor does the industry-wide net interest margin establish that a particular $5,000 checking balance “covers the account”: account-service costs and how the bank deploys its funding matter. FDIC source: https://www.fdic.gov/resources/bankers/national-rates/ (fdic.gov)
Two other checks sharpen, rather than overturn, the account of how banks earn money:
- Deposit val…
Gamma · gemini-3.1-pro
Beta’s catch regarding the FDIC table’s “Treasury Yield” column is critical: the FDIC uses the effective federal funds rate for non-maturity deposits in that column, so the manuscript’s direct comparison to a 3.6% Treasury bill is technically mixing data sources. The editor must explicitly source a short-term T-bill yield outside the FDIC table to make that math work.
I will focus on the remaining unverified claims, specifically the international comparisons and the overdraft data, and offer a distinct perspective on the manuscript's vulnerabilities.
What I found on the remaining claims:
* Overdraft Concentration: The manuscript claims 9 percent of accounts paid 79 percent of all overdraft and insufficient funds fees, citing CFPB data from 2011 and 2012. This is accurately sourced to the CFPB's August 2017 Data Point: "Frequent Overdrafters" report (page 12), which states exactly this distribution.
* EU Interchange Cap: The manuscript states EU debit card interchange has been capped since 2015 at 0.2 percent. This is entirely accurate. The European Union's Interchange Fee Regulation (IFR), which took effect in 2015, explicitly capped consumer debit card intercha…
Researcher · gemini-3-7-flash
Here is the factual verification of the open items, data points, and legal authorities cited in the manuscript and debater turns:
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1. Verification of Key Claims and Data Points
* FDIC Rates & Treasury Yield Comparison:
* Finding: As confirmed in the FDIC Monthly Update table for September 2026, the national average rate for Interest Checking is 0.07%.
* Caveat: Beta's correction is strictly accurate: footnote 3 of the FDIC National Rates methodology specifies that for non-maturity deposit products (such as checking and savings accounts), the rate listed in the "Treasury Yield" column is tied to the effective federal funds rate, not a published Treasury obligation yield. Sourcing a 3.6% yield as a "Treasury bill" directly from that FDIC checking row is technically a misattribution and requires a separate short-term Treasury benchmark source.
* *Source:* FDIC National Rates and Rate Caps
* Deposit Value (Egan, Lewellen, and Sunderam):
* Finding: Confirmed verbatim. In *The Cross-Section of Bank Value* (published in *The Review of Financial Studies*, Vol. 35, I…
The Arbiter · gpt-6-sol
Round record. The participants agree on the basic answer: a bank can earn money from a checking account with no monthly fee through low-cost deposits, debit-card interchange, fees paid by some customers, and the possibility of selling other banking products. They also agree that the manuscript overstates what those sources prove about *every* free account.
- Deposit income: Beta identified, and the Researcher confirmed, a consequential attribution error. For checking accounts, the FDIC table’s “Treasury Yield” column uses the effective federal funds rate, not a Treasury-bill yield. The $5,000 illustration’s arithmetic is correct ($3.50 at 0.07%; $180 at an assumed 3.6%), but the Treasury comparison needs an independently sourced bill rate. Neither that illustration nor an industry-wide margin proves that a particular account covers its servicing costs. Alpha and the Researcher confirmed the FDIC’s Q2 2026 net interest margins of 3.32% industry-wide and 3.81% for community banks. FDIC rate methodology: https://www.fdic.gov/resources/bankers/national-rates/ (fdic.gov)
- Value of deposit…
The Arbiter's Final Verdict · gpt-6-sol
A “free” checking account usually means no monthly account fee, not that the bank earns nothing from it.
The main potential source of income is your deposit balance. Checking accounts often pay little or no interest, while a bank can earn interest by lending or investing the money it takes in. That spread helps fund the account, although the bank must also pay for staff, technology, fraud prevention, and other costs. It does not follow that every individual account is profitable.
Banks can also earn interchange fees when you use a debit card. In the US, debit interchange is capped for large banks; smaller issuers are generally exempt, which makes card use especially important to some banking apps and their partner banks. Other revenue can come from overdraft and related fees, but those fees fall disproportionately on a minority of customers, and from customers who later take out a loan, credit card, or other product.
So the short answer is: low-cost deposits, card transactions, some account fees, and the broader customer relationship. The relative importance of each varies by bank and by customer. The FDIC’s 2026 average of 0.07% for *interest checking* i…
