What EFFR Measures—and What It Leaves Out
This chapter focuses on the market machinery behind the effective federal funds rate (EFFR): how the Federal Reserve’s post-crisis operating framework changed overnight trading, and how the composition of that trading determines what the headline rate can see. The goal is not to revisit the definition of EFFR, but to understand why a rate can remain stable as an aggregate policy benchmark while still providing an incomplete view of smaller-bank funding conditions.
From scarce reserves to administered rates
Before the Global Financial Crisis, the federal funds market operated in a scarce-reserves environment. Banks held reserve balances at the Federal Reserve, but the total quantity was limited relative to the banking system’s routine needs. A bank that ended the day short of the balance it wanted could borrow overnight from another bank with a surplus. The Federal Reserve adjusted the quantity of reserves through daily open-market operations, and the resulting trading activity helped move the federal funds rate toward the policy target.
This older framework gave the federal funds market a particular appearance. Bank-to-bank transactions were central because the marginal value of an additional reserve balance could change sharply near the end of the day. A small change in the supply of reserves could alter how urgently banks searched for funds, and the overnight rate carried information about that competition. The market was not simply a place where a pre-set policy rate was reported; it was also part of the mechanism through which the policy rate was discovered and implemented.
The financial crisis changed the scale of the balance sheet and, with it, the operating problem. Large-scale asset purchases left the banking system with far more reserve balances. In an ample-reserves framework, the Federal Reserve does not need to fine-tune the quantity of reserves every day to keep overnight rates near the desired level. Instead, administered rates—especially interest on reserve balances (IORB) and the overnight reverse repurchase agreement (ON RRP) rate—provide reference points that anchor short-term interest rates.
The practical change is easy to state but easy to misread. The Fed’s ability to keep a broad overnight benchmark stable no longer depends on making reserves scarce enough to force every bank into an active daily search for them. The EFFR can therefore remain well controlled even when the total reserve stock is large. That says something important about monetary-policy implementation. It says less about whether the last dollar of liquidity is equally accessible to every institution, or whether every bank faces the same price when it needs funds at a particular time.
The administered-rate framework also changes how to interpret sensitivity. In a scarce-reserves regime, a change in aggregate reserves could quickly affect the market-clearing pressure visible in the overnight rate. In an ample-reserves regime, the aggregate rate can be less responsive because the system as a whole has a substantial reserve cushion and the Federal Reserve’s administered rates do more of the anchoring work. A bank or network with a thinner practical cushion can still experience a different marginal condition inside that broad environment.
The difference is easiest to see at the level of the last transaction rather than the system total. If the banking system has a large quantity of reserves, the total may look comfortable even when a particular institution cannot immediately use all of them. Balances may be held by institutions with different needs, and the institutions that can lend are not necessarily the institutions that need to borrow at that moment. The ample-reserves framework reduces the pressure for the entire system to compete for reserves, but it does not erase the relationships through which particular banks obtain them.
IORB and ON RRP matter in this setting because they give market participants administered reference points for short-term funding and investment decisions. The Federal Reserve can adjust those rates to anchor the broad market instead of depending only on a daily scarcity signal. That makes the framework more predictable at the aggregate level. It also means that a stable EFFR may tell us more about the success of the anchor than about the distribution of liquidity within the system.
That is the first distinction to carry forward: aggregate rate control and uniform liquidity are related, but they are not the same achievement. The EFFR can be stable because the operating framework is working as designed, while a smaller segment of the banking system becomes more sensitive to its own reserve position, funding relationships, or access constraints.
The sequence below is a simplified map of that arrangement. It does not mean that the Federal Reserve directly sets the price of every transaction or that every lender responds in the same way. It shows why administered reference rates, different lender populations, and the final daily summary belong in the same explanation.
The last line is the crucial one. EFFR is not formed by giving each institution an equal vote. It is formed from transactions, and the weight attached to those transactions affects which conditions sit near the center of the reported distribution.
The market EFFR summarizes
The federal funds label can suggest a market dominated by banks lending to one another. The trading data described in the Federal Reserve note show a different composition. Non-bank lenders, particularly the Federal Home Loan Banks (FHLBs), account for more than 90 percent of lending cited in the note. The reported daily volume of traditional interbank trading is much smaller, ranging from about $2 billion to $6 billion.
The more-than-90-percent figure should be read as a description of the market composition documented by the note, not as a claim that every lender uses identical terms or that the same proportion determines every day’s conditions. Its importance is structural. When one class of lender supplies most of the observed volume, its borrowers and pricing environment have disproportionate influence over a statistic built from that volume. A smaller channel can still be economically important while having limited power to move the aggregate median.
The $2 billion-to-$6 billion interbank range creates the other side of the comparison. It is not zero, and it is not necessarily uninformative. It is a smaller field in which the borrowers, lenders, and reserve relationships may be more closely connected to community and regional banks. The key issue is not whether that field is large enough to dominate EFFR. It is whether it is close enough to the institutions under examination to reveal a condition that the dominant field does not represent as directly.
This does not turn the EFFR into an irrelevant number. It clarifies its population. If non-bank lenders supply most of the observed volume, their transactions have a strong influence on the daily rate. The EFFR is then primarily a summary of the conditions under which that high-volume activity occurs, including the conditions facing the bank borrowers that participate in it. It can be stable while a lower-volume set of bank-to-bank transactions moves differently.
The distinction between “large” and “small” here is not only about institution size. It is also about market participation. A community bank can matter greatly to its own depositors and local economy while contributing few transactions to the distribution from which EFFR is calculated. A network of such banks may have a shared funding need that is economically important but statistically underrepresented in the market-wide median. Their funding conditions can become more informative through an intermediary that specializes in serving them than through a rate dominated by other lenders.
A stylized example makes the weighting issue concrete. Suppose a market contains a large set of overnight transactions from one lender population whose rates remain close together, plus a smaller set of transactions from borrowers facing a higher marginal cost. If the second set is small relative to the first, its higher prices may have little effect on the median that summarizes the full market. That does not mean the higher prices are unimportant to the borrowers paying them. It means the market-wide statistic is answering a question about the center of all observed volume, not about the most exposed borrower.
The same logic explains why the phrase “the federal funds rate” needs a qualifier. A rate can be a reliable indicator of the transactions included in its calculation and still be a weak indicator for transactions that are sparse, routed through a specialized intermediary, or governed by different liquidity constraints. Accuracy concerns whether the statistic is computed correctly. Representativeness concerns whether the statistic is the right lens for the question at hand.
This boundary runs in both directions. A calm EFFR does not establish that smaller-bank funding is comfortable, but a high rate in a smaller segment would not establish that the entire federal funds market is under the same pressure. The observation must be matched to the population that generated it. It also must be compared with the reference that gives it meaning: an aggregate rate with its policy anchor, or a segment rate with the reserve conditions and borrower relationships of that segment.
For the same reason, a useful analysis should resist treating “smaller banks” as one uniform block. Some institutions may borrow through the observed channel; others may rely more on deposits, correspondents, or FHLB advances. The Federal Reserve note supports a signal about the bankers’ bank network and the smaller-bank conditions connected to it. It does not provide a bank-by-bank census or prove that every community institution moves with the BFFR.
The Federal Reserve note’s reported composition also explains why EFFR can remain relatively calm during an episode that affects smaller banks. FHLBs and other non-bank lenders are not simply a statistical nuisance; they are an important part of the market’s functioning. Their volume can help keep the aggregate distribution anchored even as a residual interbank channel reflects different reserve demand. The two conditions can coexist because the lenders, borrowers, and balance-sheet relationships are not identical.
This is why it would be a mistake to describe the situation as EFFR “missing” information in the sense of being improperly calculated. The information is outside the rate’s strongest field of view. A market-wide measure compresses many transactions into one number, which makes it useful for tracking a broad condition but necessarily removes some distinctions. The question is whether the removed distinctions matter for the decision being made.
A benchmark becomes misleading only when its scope is silently expanded. If the question is whether the broad overnight market remains anchored, EFFR’s aggregate construction is a feature. If the question is whether a community bank can meet an immediate funding need without paying a premium, the relevant evidence may sit in a narrower transaction set. The same reported stability can therefore support a sound conclusion in one context and an incomplete conclusion in another. The analytical error is not using EFFR; it is asking it to answer a question its construction was not designed to answer.
For monetary-policy implementation, a stable EFFR may be exactly the relevant outcome. For assessing whether smaller banks are paying more to obtain overnight liquidity, it may be insufficient. The first question concerns control of an aggregate benchmark. The second concerns the marginal price and reserve position of a particular intermediation network. A single number should not be expected to settle both.
The next institution to examine is the bankers’ bank because it connects the lower-volume segment to a specific source of information. Bankers’ banks serve community and regional banks, lend primarily to depository institutions, and can pool customers’ excess reserves. That arrangement gives their transactions a different economic meaning from the high-volume activity that dominates EFFR. The issue is no longer simply what the headline rate leaves out, but how the omitted channel produces its own observable rate.