Most people never hear about SOFR, yet trillions of dollars of loans, bonds and derivatives are priced from it every day. The Secured Overnight Financing Rate is the main benchmark for short-term US dollar borrowing, and when it moves unexpectedly, it can be a sign of strain in the plumbing of the financial system.
What SOFR measures
SOFR is the cost of borrowing cash overnight using US Treasury securities as collateral. These deals happen in the repurchase, or repo, market, where one party sells Treasuries and agrees to buy them back the next day at a slightly higher price. The difference works out as an interest rate.
The Federal Reserve Bank of New York publishes SOFR each business morning. It is based on actual transactions, typically more than a trillion dollars a day, which makes it hard to manipulate.
Why it replaced LIBOR
For decades, the London Interbank Offered Rate, or LIBOR, was the world’s main borrowing benchmark. It was based on banks’ estimates of what they would pay to borrow, not on real trades. After the LIBOR scandal revealed that some banks had manipulated their submissions, regulators pushed for alternatives built on real transactions.
In the US that alternative became SOFR. Dollar LIBOR was phased out by mid-2023. The UK equivalent is SONIA, the Sterling Overnight Index Average, which plays a similar role for sterling.
What moves SOFR
SOFR mostly follows the Federal Reserve’s policy rate. When the Fed raises or cuts its target range, SOFR moves with it. Day to day, it usually sits close to the interest the Fed pays on reserves and its overnight reverse repo rate.
But SOFR can also move because of supply and demand for cash and collateral. Large Treasury issuance, quarterly corporate payment dates, month-end and quarter-end balance sheet management by banks, and the Fed’s own balance sheet policy all influence it. When cash becomes scarce, SOFR can rise above the Fed’s target range, a warning sign that funding markets are stretched.
The September 2019 episode
The clearest example came in September 2019, when overnight repo rates spiked to around 10% at one point, far above the Fed’s target. A mix of corporate payments, Treasury settlement and low bank reserves left too little cash in the system. The Fed stepped in with emergency repo operations. The episode showed that SOFR is not just a technical rate; it is a gauge of financial system liquidity.
Why traders care
SOFR futures and options are among the most traded interest rate contracts in the world. Traders use them to bet on, or protect against, future Fed decisions. The prices of these contracts reveal what the market expects the Fed to do over the coming months and years.
Mortgages, corporate loans and floating-rate bonds are increasingly priced off SOFR, so changes in the rate feed directly into borrowing costs. Watching the gap between SOFR and the Fed’s target range also helps traders spot funding stress before it spreads to other markets, such as FX funding.
Limits to keep in mind
SOFR is an overnight secured rate, so it does not include a premium for bank credit risk. Some lenders prefer measures that do, which is why alternative benchmarks exist. SOFR can also jump around on specific calendar dates without signalling anything serious.
Our assessment is that SOFR is worth watching mainly at two levels: as the anchor for Fed expectations through futures pricing, and as an early warning of funding stress when it drifts above the policy range. Quarter-end moves deserve attention but not alarm unless they persist. A sustained gap above the Fed’s range would be a clear reason for caution across risk assets. If you want to understand how you read macro signals like these, our free trader assessment is a sensible next step.
