TL;DR
- The Secured Overnight Financing Rate (SOFR) is the benchmark interest rate that replaced LIBOR as the global standard for pricing trillions of dollars in loans, mortgages, and derivatives
- SOFR is based on actual overnight Treasury repo transactions — real trades, not bank estimates
- The switch from LIBOR to SOFR happened because LIBOR was manipulated by the banks that reported it; SOFR can't be gamed the same way
- When SOFR moves, it ripples through adjustable-rate mortgages, corporate loans, and floating-rate debt across the economy
What Is SOFR — The Simple Version
Imagine a massive overnight lending market where banks and financial institutions borrow cash by temporarily handing over U.S. Treasury bonds as collateral. Every morning, thousands of these transactions settle. SOFR is simply the weighted average interest rate on all of those trades — the going rate for overnight money, backed by the safest collateral on earth.
That's it. No committee. No estimates. No phone calls between traders deciding what the rate "should" be. Just the price that trillions of dollars in real transactions actually cleared at.
The Secured Overnight Financing Rate is published daily by the New York Fed, calculated from Treasury repurchase agreement (repo) transactions — the plumbing of the financial system. When a money market fund lends cash to a bank overnight and takes Treasuries as collateral, that's a repo trade. SOFR is the aggregate price of those trades.
SOFR replaced LIBOR — the London Interbank Offered Rate — as the dominant benchmark for U.S. dollar-denominated financial contracts. LIBOR had been the global benchmark for decades, used to price everything from student loans to $400 trillion in derivatives. The problem: it was based on what banks said they could borrow at, not what they actually paid. That distinction turned out to matter enormously.
Why SOFR Matters for Investors
If you have an adjustable-rate mortgage, a variable-rate student loan, a corporate bond with a floating coupon, or exposure to interest rate swaps — SOFR is already in your financial life whether you know it or not.
Here's the cause-and-effect chain that matters: when the Fed tightens monetary policy and overnight rates rise, SOFR rises with them. That increase passes directly into any financial contract indexed to SOFR. A business that borrowed at SOFR + 2% in 2021 when SOFR was near zero suddenly faced a dramatically higher interest bill when SOFR climbed above 5% in 2023. That's not an abstraction — it's cash out the door every quarter.
For equity investors, SOFR matters as a leading indicator of credit stress. When SOFR spikes relative to the Fed's target range, it signals stress in the repo market — the plumbing is backing up. The repo market is where banks fund themselves overnight. If that market seizes, credit tightens fast, and risk assets feel it quickly.
The 2019 repo market disruption is the textbook example. In September 2019, overnight repo rates spiked from roughly 2% to above 10% in a single day — a sign that bank reserves had been drained too far. The Fed had to intervene with emergency repo operations. SOFR reflected that stress in real time. LIBOR, being a survey rate, would have lagged the signal by days.
For fixed income investors, SOFR-linked floating rate notes and CLO tranches are now the standard. Understanding where SOFR is and where it's likely to go is the same as understanding your coupon income on a significant portion of the investment-grade floating rate market.
How SOFR Works — The Details
The repo market is the financial system's overnight plumbing. Every day, institutions with excess cash (money market funds, banks, asset managers) lend it out against Treasury collateral. Institutions that need cash (dealers, hedge funds, banks funding their balance sheets) borrow it. The interest rate on those loans is what SOFR measures.
The New York Fed collects transaction data from three types of repo markets:
- Tri-party repo (cleared through Bank of New York Mellon)
- General collateral finance (GCF) repo
- Bilateral Treasury repo (cleared through the DTCC's Fixed Income Clearing Corporation)
Each day's SOFR is a volume-weighted median of all eligible transactions — not a mean, which would be skewed by outliers. The volume-weighted median means the rate reflects where the bulk of actual money traded, not where a few unusual transactions cleared.
The formula in plain terms: SOFR = volume-weighted median rate across all qualifying overnight Treasury repo transactions settled that day.
Why "secured" matters: The "S" in SOFR is doing heavy lifting. Because these loans are collateralized by U.S. Treasuries, SOFR carries essentially no credit risk. LIBOR, by contrast, was unsecured — it reflected not just the time value of money but also the perceived credit risk of the banks borrowing. That credit risk component made LIBOR jump during stress events (it spiked dramatically in 2008), conflating credit stress with pure interest rate levels. SOFR strips that credit risk out.
Term SOFR: The original SOFR is overnight only. But most loans need a term rate — something that tells a borrower what their rate is for the next 30, 90, or 180 days. The CME Group now publishes Term SOFR rates (1-month, 3-month, 6-month, 12-month) derived from SOFR derivatives markets. Most corporate loans and mortgages use Term SOFR, not overnight SOFR directly.
Compounded SOFR: For derivatives and some bonds, daily overnight SOFR readings are compounded over the relevant period. A 3-month compounded SOFR takes each day's overnight rate, compounds them together, and produces an effective rate for the period. This approach is more precise but operationally complex — which is why Term SOFR became the practical standard for lending markets.
Where SOFR sits in the rate stack: SOFR trades very close to the Fed's policy rate. With RRP at $0B as of late March 2025 — meaning the Fed's overnight reverse repo facility has been fully drained — there's no longer a technical floor keeping SOFR pinned near the bottom of the Fed's target range. SOFR now floats freely within the range, tracking closely to the interest on reserve balances (IORB) rate.
How to Use This in Your Investing
SOFR is most useful as a real-time read on short-term funding stress and Fed policy transmission.
Watch for SOFR spikes above the Fed's target range. When SOFR trades materially above the top of the Fed funds target range, it signals that overnight funding markets are under pressure. That's a yellow flag for risk assets — historically, repo market stress precedes broader credit tightening by days to weeks.
Use SOFR to price floating-rate exposure. If you hold floating-rate bonds, CLO tranches, or bank loans, your income is directly tied to where SOFR settles each period. Tracking SOFR against Fed rate expectations tells you whether your coupon income is likely to rise, fall, or hold steady.
SOFR as a liquidity cross-check. At Acid Capitalist, we track net liquidity — the Fed balance sheet minus TGA minus RRP — as the primary signal for market conditions. SOFR is a complementary read on the short end of that picture. When net liquidity is compressing (as it has been with the Fed's QT program) and SOFR starts drifting higher within the target range, that's the plumbing showing early signs of tightness. You can track the full liquidity picture on AC's AC Signal dashboard, which monitors the Fed balance sheet, TGA, and RRP in real time.
What to watch: SOFR trending toward the top of the Fed's target range, widening SOFR-OIS spreads, or any sudden intraday spikes in repo rates. These are the early warning signals that the plumbing is backing up before the mainstream media notices.
FAQ
Q: What's the difference between SOFR and the federal funds rate? A: The federal funds rate is the rate banks charge each other for overnight unsecured loans of reserve balances held at the Fed. SOFR is the rate on overnight secured loans backed by Treasury collateral. Both are overnight rates that move with Fed policy, but SOFR reflects the repo market specifically. In normal conditions they track closely; during stress events, they can diverge.
Q: Does SOFR affect my mortgage? A: If you have an adjustable-rate mortgage (ARM) originated after mid-2023, it's almost certainly indexed to Term SOFR rather than LIBOR. When SOFR rises, your rate adjustment at reset will be higher; when SOFR falls, it adjusts down. Fixed-rate mortgages are not directly affected by SOFR moves.
Q: Why did LIBOR get replaced — wasn't it working? A: LIBOR worked until it didn't. The 2012 LIBOR manipulation scandal revealed that major banks were submitting false rates to benefit their derivatives trading desks. Because LIBOR was a survey — banks reporting what they thought they could borrow at — it was structurally vulnerable to manipulation. SOFR is based on actual transactions, making that kind of manipulation essentially impossible at scale.
Q: Is SOFR risk-free? A: SOFR is often called a "risk-free rate" because it's secured by U.S. Treasury collateral, which carries no credit risk in practical terms. But "risk-free" refers to credit risk specifically — SOFR still moves with interest rate risk. If the Fed raises rates, SOFR rises. The rate itself is not fixed or guaranteed.
Q: Where can I find the daily SOFR rate? A: The New York Fed publishes SOFR each business day at approximately 8:00 AM Eastern time on their website. Term SOFR rates are published by the CME Group. For context on how SOFR fits into the broader liquidity picture, the AC Signal dashboard tracks the key variables that drive short-term rate dynamics.