A SOFR overnight index swap is an interest rate swap in which one party pays a fixed rate and the other pays a floating rate built by compounding the daily Secured Overnight Financing Rate over each accrual period. No principal changes hands. Since panel-based USD LIBOR settings ceased on June 30, 2023, the SOFR OIS has become the dominant format for pricing and hedging US dollar interest rate exposure, and its curve now supplies the discount factors used across essentially all cleared US dollar derivatives.1Financial Conduct Authority. The US Dollar LIBOR Panel Has Now Ceased
The Rate Underneath the Swap
SOFR measures the cost of borrowing cash overnight against U.S. Treasury collateral. Because the loans are secured, the rate carries far less credit risk than LIBOR did, and it doesn’t widen when banks’ unsecured funding costs rise. The Federal Reserve Bank of New York publishes SOFR each business day from transaction data in the Treasury repurchase agreement market cleared through the Fixed Income Clearing Corporation.2Federal Reserve Bank of New York. Secured Overnight Financing Rate Data
The volume behind the rate is enormous. Daily transactions routinely exceed $2 trillion and have recently surpassed $3 trillion, giving the benchmark a depth LIBOR never had.3Federal Reserve Bank of St. Louis. Secured Overnight Financing Volume (SOFRVOL) SOFR is also more volatile than the effective federal funds rate it replaced as the standard overnight index, particularly at quarter-end and year-end when repo dynamics shift.
How the Two Legs Work
The fixed rate on a SOFR OIS is locked in at trade date and remains constant for the life of the swap. The floating rate isn’t known until the end of each accrual period, because it’s built by compounding each day’s published SOFR reading over that period. This “in arrears” structure is fundamental to how OIS contracts price.
Payment frequency depends on maturity. For shorter swaps, both legs commonly pay quarterly or annually on an actual/360 day count. On longer-dated trades, the fixed leg often pays semi-annually with a 30/360 day count while the floating leg continues on actual/360.4CME Group. Pricing and Hedging USD SOFR Interest Rate Swaps with SOFR Futures The floating leg always uses actual/360 because that is the standard US money market convention.5Federal Reserve Bank of New York. An Updated User’s Guide to SOFR
On each payment date, the two sides calculate what they owe under their respective legs and settle the net difference. The fixed payer wins if compounded SOFR over the period comes in above the fixed rate; the floating payer wins if it comes in below.
Reading the Fixed Rate
The fixed rate on a SOFR OIS embeds the market’s consensus forecast for overnight rates over the swap’s life. A two-year OIS trading below current SOFR implies traders expect cuts; a two-year OIS above current SOFR implies expected hikes. The OIS curve is therefore one of the most watched indicators of Federal Reserve rate expectations.
Compounding, Lookbacks, and Observation Shifts
The floating leg’s compounding works by applying each day’s SOFR to the notional, then folding that day’s interest into the base for the next day. Over a quarterly period, roughly 60 to 65 business days of SOFR readings compound together. The result runs slightly higher than a simple average of the same readings because of the interest-on-interest effect.
A practical problem falls out of this design. The final SOFR reading in any accrual period isn’t published until the next business day, which would leave the counterparties without time to settle. Two conventions solve the timing issue.
- Lookback: each day’s interest calculation uses the SOFR reading from a set number of business days earlier. The standard default is five business days.
- Observation period shift: the entire observation window shifts back by a set number of business days relative to the accrual period. The default is again five business days, matching the lookback convention.
Both approaches ensure the full floating payment is known several days before it’s due. The five-business-day default is set by the 2021 ISDA Interest Rate Derivatives Definitions and applies whenever a confirmation doesn’t specify otherwise.6International Swaps and Derivatives Association. Documenting RFR Derivatives Using Different Approaches to Compounding/Averaging Under the 2006 ISDA Definitions The 2021 ISDA Definitions, which are separate from the ISDA Master Agreement, govern the specific rate calculation, compounding method, and fallback mechanics for SOFR OIS contracts.
Pricing and the SOFR OIS Curve
At initiation, the fixed rate is set so that the present value of the expected fixed payments equals the present value of the expected floating payments. Neither side has an edge at trade date. Getting to that equilibrium requires both a forecast of future SOFR readings and a way to discount the resulting cash flows.
Both come from the same tool. The SOFR OIS curve is built from observed fixed rates on OIS contracts across the maturity spectrum. Dealers extract implied forward SOFR rates from those prices, which serve as the projection of what SOFR will be on each future date. The same curve supplies the discount factors used to bring the projected cash flows back to today.
This dual role is why the SOFR OIS curve sits at the center of the market’s plumbing. In mid-2020, CME and LCH switched their clearing houses to SOFR-based discounting and price alignment interest, replacing the fed funds OIS curve that had previously served that purpose. The SOFR OIS curve is now the standard discount curve for cleared US dollar derivatives generally, not just for SOFR swaps.
Once a swap is on the books, its value changes as the curve moves. A party that locked in a low fixed rate gains value if the curve shifts up, because the market would now demand a higher fixed rate for the same tenor. Mark-to-market valuations use the current curve to re-project floating cash flows and re-discount everything, producing the swap’s net present value.
Liquidity and Hedging Uses
The SOFR OIS market is the deepest segment of the US dollar derivatives landscape. In the second half of 2024, roughly $39.3 trillion in notional traded. About 41% had a tenor of one year or less, 38% ran between one and five years, and 20% extended beyond five years. Liquidity runs across the curve rather than clustering in a narrow band.
For hedging, the mechanics are direct. A bank holding SOFR-indexed floating-rate loans might enter an OIS paying fixed and receiving compounded SOFR. Its floating loan income and its floating OIS receipts offset, leaving a net fixed-rate position. The spread between the OIS fixed rate and a bank’s actual unsecured funding cost gives a live read on credit and liquidity conditions, functioning much like the old TED spread.
The short end of the OIS curve is widely treated as the best available proxy for the US dollar risk-free rate. That status flows from SOFR’s Treasury collateral backing and the trading volume behind the swaps. Algorithmic activity at the short end keeps bid-ask spreads tight.
Clearing, Margin, and Reporting
Most standardized SOFR OIS contracts have to be centrally cleared. Under CFTC rules, US dollar OIS referencing SOFR with maturities from seven days to 50 years fall within the mandatory clearing requirement.7eCFR. 17 CFR 50.4 – Classes of Swaps Required to Be Cleared The clearing counterparty sits between the two sides, absorbing counterparty credit risk. Both parties post initial margin at trade date and exchange variation margin daily as the swap’s value moves. Those variation margin calculations rely on the SOFR OIS curve for discounting.
Trades outside the clearing mandate, typically customized structures, still face margin obligations. Since September 2022, any firm with an aggregate average notional amount of uncleared derivatives above $8 billion must post initial margin on those trades. That final phase of the global uncleared margin rules brought hundreds of additional firms into scope.
Every swap transaction must be reported to a swap data repository as soon as technologically practicable after execution.8eCFR. Part 43 – Real-Time Public Reporting Public dissemination follows with time delays that depend on the trade type:
- Block trades on a swap execution facility: 15-minute delay.
- Large notional off-facility swaps with at least one swap dealer: 15 to 30 minutes, depending on whether the swap is subject to mandatory clearing.
- Large notional off-facility swaps with no swap dealer on either side: one hour if subject to mandatory clearing, or 24 business hours if not.
Notional amounts above set thresholds are capped in public reports. For interest rate swaps, those caps are $250 million for tenors up to two years, $100 million for tenors between two and ten years, and $75 million for tenors beyond ten years.8eCFR. Part 43 – Real-Time Public Reporting
Fallbacks and Legacy LIBOR Contracts
Contracts that transitioned from LIBOR carry hardwired fallback language that establishes a waterfall. When USD LIBOR permanently ceased or was declared non-representative, the contract automatically shifted to a replacement rate plus a fixed spread adjustment.9Federal Reserve Bank of New York. ARRC Supplemental Recommendations of Hardwired Fallback Language for LIBOR Syndicated and Bilateral Business Loans
The spread adjustments compensate for the fact that SOFR and LIBOR don’t measure the same thing. LIBOR included a bank credit premium that SOFR lacks. The ARRC and ISDA adopted fixed spread values calculated from the historical median difference between the two rates:
- One-month tenor: 11.448 basis points.
- Three-month tenor: 26.161 basis points.
- Six-month tenor: 42.826 basis points.
These adjustments are permanent.9Federal Reserve Bank of New York. ARRC Supplemental Recommendations of Hardwired Fallback Language for LIBOR Syndicated and Bilateral Business Loans If the replacement rate is itself ever discontinued or declared non-representative, the same waterfall triggers again to find the next suitable rate.
Tax Treatment of Transitioned Contracts
Replacing LIBOR with SOFR in an existing contract would ordinarily raise the question of whether the change is a taxable exchange. The IRS answered that directly. Under Treasury Regulation Section 1.1001-6, a “covered modification” that replaces a discontinued interbank offered rate with a qualified rate such as SOFR is not treated as a taxable exchange.10eCFR. 26 CFR 1.1001-6 – Transition From Certain Interbank Offered Rates
To fall within the safe harbor, the modification must do one of three things: replace the operative LIBOR-based rate with SOFR or another qualified rate, add SOFR as a fallback to an existing LIBOR reference, or replace an existing LIBOR-based fallback with a SOFR-based one. Related adjustments, such as a one-time compensating payment or a spread tweak to maintain economic equivalence, are also covered, provided the modification doesn’t fall into the regulation’s exclusions.10eCFR. 26 CFR 1.1001-6 – Transition From Certain Interbank Offered Rates The qualified rate must reference transactions in the same currency as the discontinued rate; SOFR qualifies for any USD LIBOR replacement.
Without this relief, every legacy LIBOR swap, loan, or bond that transitioned to SOFR could have triggered gain or loss recognition for both counterparties on a change that was economically neutral by design.