SOFR vs. Treasury Bills: Money Market Spreads Explained

In wholesale capital markets, understanding the cost of cash requires looking beneath benchmark policy rates. For decades, investors tracked the “TED spread”—the difference between three-month interbank borrowing rates and risk-free Treasury bills—as Wall Street’s primary barometer of banking panic. Today, following global benchmark reform and the retirement of unsecured LIBOR, market participants look to the spread between the Secured Overnight Financing Rate (SOFR) and short-term Treasury bill yields to gauge liquidity conditions, balance-sheet constraints, and supply dynamics across short-term funding markets.

Here is what every capital markets participant needs to know about the modern SOFR-Treasury relationship, why it replaced the traditional TED spread, and what shifts in money-market spreads reveal about underlying financial plumbing.

What Is the SOFR-Treasury Spread?

The SOFR-Treasury spread measures the difference between overnight secured financing rates and the yields on risk-free, short-term government debt. Rather than reflecting unsecured bank insolvency risk, this spread reflects supply-demand balances in collateralized repo markets relative to sovereign cash instruments.

To unpack this relationship, we must examine the two underlying instruments:

• Secured Overnight Financing Rate (SOFR): According to the Federal Reserve Bank of New York, “the Secured Overnight Financing Rate (SOFR) is a broad measure of the cost of borrowing cash overnight collateralized by Treasury securities.” Because SOFR is anchored in over a trillion dollars of daily repo transactions, it is virtually free of credit risk, reflecting the cost of collateralized liquidity among primary dealers, money funds, and clearinghouses.
• Treasury Bills (T-Bills): Managed by the U.S. Department of the Treasury via TreasuryDirect, short-term sovereign obligations differ structurally from loans: “bills are sold at a discount or at par (face value). When the bill matures, you are paid its face value.” T-bills represent direct obligations of the U.S. government, providing pristine credit safety and zero capital-adequacy haircut requirements for institutional balance sheets.

In normal conditions, an overnight secured rate like SOFR trades closely in line with the target policy range established by the Federal Reserve, which also tracks the Federal Reserve Board H.15 release, where “the daily effective federal funds rate (EFFR) is a volume-weighted median of transaction-level data collected from depository institutions” in domestic unsecured overnight funding.

Why Did Markets Move Away from the TED Spread?

To grasp why money-market analysts evaluate the SOFR-Treasury dynamic, one must understand the structural flaws of its historical predecessor: the TED spread.

The acronym “TED” originated from “Treasury” and “ED” (the ticker for Eurodollar futures contracts). Mathematically, it was defined as:

In theory, because the London Interbank Offered Rate (LIBOR) reflected the rate at which major global banks lent cash to one another on an unsecured basis, an expanding TED spread signaled that banks suspected counterparties might face insolvency. During the 2008 global financial crisis, the TED spread surged beyond 450 basis points (4.50 percentage points) as private interbank lending completely froze.

However, the TED spread became obsolete due to two primary realities:

1. Unsecured Interbank Lending Evaporated: Following post-crisis liquidity mandates, commercial banks largely abandoned unsecured term lending to one another, choosing instead to transact in secured repurchase agreements or hold reserves at the central bank. Consequently, LIBOR quotes ceased to reflect real transaction volumes and became subjective panel estimates vulnerable to manipulation.
2. The Shift to Robust Secured Reference Rates: Financial regulatory bodies worldwide mandated transitioning away from panel-based rates toward robust, transaction-backed benchmarks. In the United States, the Alternative Reference Rates Committee (ARRC) selected SOFR as the definitive replacement.

How the Secured Spread Differs: Counterparty Risk vs. Collateral Friction

Unlike the historical TED spread, the spread between SOFR and Treasury bills does not measure commercial bank default probability. Because transactions contributing to SOFR are backed by Treasury securities, credit risk is neutralized.

Instead, fluctuations between SOFR and short-term T-bill yields reflect balance sheet capacity and collateral scarcity. When primary dealers absorb heavy Treasury auction issuance, dealer balance sheets become congested with debt securities. Dealers require cash financing, pushing overnight repo demand—and thus SOFR—higher relative to cash instruments.

Worked Example: Calculating and Interpreting the Spread

To see how this works in practice, consider a clear worked example with hypothetical inputs representing institutional money-market rates:

Common Misconceptions to Avoid

When tracking short-term funding metrics, institutional traders and retail investors frequently stumble over three common pitfalls:

• Confusing Secured Repo Dislocation with Bank Insolvency: A sudden spike in SOFR (such as the historic September 2019 repo squeeze) does not mean a commercial bank is failing. It typically means that settlement flows, corporate tax deadlines, and Treasury settlement schedules pulled cash out of the banking system faster than reserves could redistribute.
• Ignoring Term Structure Differences: SOFR is fundamentally an overnight rate, whereas Treasury bills are commonly quoted in 4-week, 8-week, 13-week (3-month), 26-week (6-month), or 52-week (1-year) tenors. Comparing overnight SOFR to a 6-month T-bill introduces duration risk and interest-rate expectations rather than pure liquidity friction. To make a pure comparison, analysts either compound overnight SOFR into a term index or evaluate Term SOFR rates.
• Discount Basis vs. Investment Yield: As detailed by TreasuryDirect, Treasury bills are quoted on a discount basis (using a 360-day year and face value). Before comparing a T-bill rate to SOFR (which is an interest-bearing rate), the bill discount rate must be converted into a bond-equivalent investment yield using actual days to maturity.

What to Watch Next in Short-Term Capital Markets

As the Federal Reserve manages quantitative tightening (QT) and balance sheet normalization, capital markets desks monitor money market spreads for early signs of reserve scarcity. Critical indicators to observe include:

1. Federal Reserve Overnight Reverse Repo (ON RRP) Take-Up: As cash in the Fed’s ON RRP facility depletes, marginal cash stays in private repo markets, keeping SOFR sensitive to net Treasury bill supply.
2. SOFR Spreads Against EFFR: When SOFR prints above the Effective Federal Funds Rate, it confirms that repo dealers are willing to pay a premium over unsecured interbank deposits to secure financing for securities inventories.
3. Treasury General Account (TGA) Rebuilding: Large Treasury bill issuance surges to fund the government account withdraw bank reserves, often exerting upward pressure on overnight repo spreads.

For additional background on fixed income mechanics and yield measurement, see our guide to Treasury bill discount rate versus investment yield and our overview on option-adjusted spreads and bond risk.

Sources & Further Reading

• Federal Reserve Bank of New York: Secured Overnight Financing Rate (SOFR) Reference Rates
• TreasuryDirect: U.S. Treasury Bills Overview, Structure, and Terms
• Federal Reserve Board: Selected Interest Rates (Daily) – Statistical Release H.15

Disclosure: This article is for informational purposes only and is not investment advice.

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