A basis swap is a contract between two parties to exchange streams of floating interest payments, with each leg tied to a different floating benchmark. Both sides float. That is what sets it apart from a plain interest rate swap, where one side pays a fixed rate against a floating one. The “basis” is the gap between the two benchmarks, and that gap is the whole reason the trade exists. Notional principal is a reference figure for calculating payments and is almost never exchanged. These contracts live in the institutional market: banks, insurers, large corporates, and dealers use them to manage the risk that two floating rates will drift apart.
How It Differs From a Standard Interest Rate Swap
In a plain-vanilla interest rate swap, one party pays fixed and receives floating, or the reverse. A basis swap replaces the fixed leg with a second floating leg pegged to a different index. The two benchmarks might come from entirely different markets, like the federal funds rate and the prime rate, or they might be different tenors of the same index, such as 3-month SOFR against 6-month SOFR. Either way, the parties are not taking a view on where rates go in general. They are focused on how the relationship between the two chosen rates behaves.
Because the notional principal never changes hands, the only money that moves is the net difference between the two floating calculations on each payment date. A $500 million notional basis swap is not a $500 million loan. That figure simply scales the interest calculations so the swap matches a real-world exposure the parties want to hedge.
How the Payments Work
Three inputs drive every basis swap: the two floating indices, the notional principal, and a fixed spread added to one leg. The spread exists so the trade is fair at inception. Without it, one side would start with a structurally better position. The spread is set so the present value of the expected cash flows on both legs is equal when the swap begins, a condition known as zero net present value at inception.
On each payment date, both sides compute what they owe using their respective index. Say Party A owes payments based on 3-month SOFR and Party B owes 6-month SOFR plus a 5-basis-point spread. Each side multiplies its rate by the notional and the fraction of the year covered. The CME Group publishes forward-looking Term SOFR reference rates for 1-month, 3-month, 6-month, and 12-month tenors, giving the market standardized benchmarks for these calculations.
Only the net amount moves. If Party A owes $1.5 million and Party B owes $1.4 million, Party A sends $100,000 to Party B and nothing else changes hands. The International Swaps and Derivatives Association describes payment netting as combining offsetting cash flow obligations between two parties on a given day in a given currency into a single net payment. This cuts settlement risk considerably.
Payments typically settle quarterly or semi-annually, depending on the agreement. The notional can also change on a schedule. An amortizing swap lets the notional decline over time, which fits a shrinking loan portfolio. An accreting swap lets it grow. These shape the size of each period’s cash flows without changing the underlying mechanics.
Common Types
Basis swaps fall into three broad groups, each addressing a different kind of mismatch.
Index-to-Index Swaps
These exchange payments tied to two different floating benchmarks. A bank might swap federal funds exposure for prime rate exposure, or trade one overnight rate for another. The two indices usually sit in different corners of the money market, with their own credit profiles and liquidity. Trading the spread between them lets institutions line up funding costs with lending revenues when those are priced off different benchmarks.
Tenor Swaps
Tenor swaps use the same underlying index but different reset periods. Trading 3-month SOFR for 6-month SOFR is the classic example. Both rates come from the same overnight secured funding market, but their pricing diverges because the longer tenor builds in more term risk and different liquidity assumptions. A bank whose assets reset every six months but whose liabilities reset every three months can use a tenor swap to close that gap.
Cross-Currency Basis Swaps
These exchange floating payments denominated in different currencies. A multinational might swap SOFR-based dollar payments for euro payments tied to the euro short-term rate (€STR). The Bank for International Settlements describes the structure: during the contract term, one party pays the floating rate in one currency while receiving the floating rate plus a spread in the other, with periodic exchanges typically every three months. Unlike single-currency versions, cross-currency basis swaps often involve an actual exchange of principal at the start and end of the contract, because the parties need the foreign currency itself, not just the rate exposure.
Why Institutions Use Them
The core use case is managing asset-liability mismatches on a bank’s balance sheet. Picture a regional bank with $500 million in commercial loans priced off the prime rate and $500 million in wholesale funding tied to the federal funds rate. Those two rates usually move together, but not perfectly. When funding costs climb faster than lending rates, the bank’s net interest margin compresses. That gap is basis risk, and it can quietly eat into earnings even when overall rates are stable.
The bank enters a basis swap: pay federal funds, receive prime, on a $500 million notional. The swap’s cash flows now offset the mismatch. If funding costs spike relative to loan income, the swap pays the difference. If the spread moves the other direction, the bank pays into the swap but earns more on its loans. Either way, the margin stays predictable.
This kind of structural hedging is the main business of basis swaps. Banks, insurance companies, and corporate treasuries use them to lock in spreads that would otherwise fluctuate. The alternative is accepting that profitability depends on two benchmarks staying in a stable relationship, which history suggests is a bad bet over multi-year horizons.
Traders also use basis swaps tactically, to express a view on how the spread between two benchmarks will change. A trader who thinks SOFR will tighten relative to the federal funds rate can enter the right basis swap and profit from that convergence without taking a directional bet on rates.
What Drives the Basis Spread
The fixed spread added to one leg is not arbitrary. It reflects several market factors and moves as conditions shift.
Liquidity differences between the two reference markets are the most consistent driver. An index tied to a deep, heavily traded market carries a tighter spread than one tied to a thinner market. The party taking the less liquid exposure demands compensation for the higher cost of trading and hedging there.
Credit risk differences matter when the two indices have different risk profiles. The transition away from LIBOR made this plain. LIBOR embedded the credit risk of interbank lending, while SOFR is a nearly risk-free rate backed by Treasury collateral. Swapping between a credit-sensitive rate and a risk-free one requires a spread that accounts for that fundamental gap. The discontinuation of the Bloomberg Short-Term Bank Yield Index on November 15, 2024 further narrowed the menu of credit-sensitive alternatives and reshaped basis swap pricing in the process.
Supply and demand imbalances also move spreads. When many institutions want to receive one index and pay the other at the same time, the spread adjusts to reflect the crowding. Regulatory changes amplify this. New capital rules or shifts in how regulators treat certain exposures can suddenly make one side more expensive, and the spread reprices.
Central bank policy expectations feed through as well. If the market anticipates a policy shift that will affect the two indices differently, that expectation gets priced into the spread right away. The basis spread functions as a forward-looking read on the relative health of different funding markets.
Clearing, Reporting, and Margin Rules
Basis swaps are over-the-counter derivatives, and the rules changed sharply after the 2008 financial crisis. The Dodd-Frank Act imposed three main requirements: mandatory clearing for standardized contracts, mandatory reporting, and margin requirements for uncleared swaps.
The Commodity Futures Trading Commission requires certain interest rate swaps to be cleared through registered derivatives clearing organizations. The clearing mandate covers fixed-to-floating swaps, basis swaps, forward rate agreements, and overnight index swaps across various currencies. For U.S. dollar instruments, overnight index swaps referencing SOFR have been subject to mandatory clearing since October 31, 2022. Basis swaps referencing certain other benchmarks, such as EURIBOR-based basis swaps in euros, are also covered by the mandate.
Central clearing cuts counterparty credit risk by inserting a clearinghouse between the two parties. The clearinghouse becomes the buyer to every seller and the seller to every buyer, and every participant posts collateral daily. Highly customized basis swaps with non-standard terms typically remain bilateral, meaning the parties face each other’s credit risk directly.
All swaps, cleared or not, must be reported to a swap data repository. For trades executed on a swap execution facility or designated contract market, the facility files the initial report. For off-facility swaps where the reporting counterparty is a swap dealer or major swap participant, the report is due by the end of the next business day. Non-dealer counterparties get an additional day. Swap dealers also report valuation, margin, and collateral data on each business day throughout the life of the swap.
Uncleared basis swaps are subject to both initial and variation margin requirements. Initial margin applies to entities whose average month-end aggregate notional of uncleared swaps exceeds $8 billion, calculated using March, April, and May figures of the relevant year. Variation margin, which covers daily changes in market value, applies more broadly. These requirements make sure both parties hold enough collateral to cover potential losses if one side defaults.
The ISDA Documentation
Nearly every basis swap in the institutional market sits under an ISDA Master Agreement. The International Swaps and Derivatives Association created this standardized contract to provide a consistent legal framework for OTC derivatives. The current version, the 2002 ISDA Master Agreement, includes provisions for measuring damages after default, force majeure events, set-off rights, and close-out netting. Close-out netting matters most of all. If a counterparty defaults, the non-defaulting party can terminate all outstanding transactions under the master agreement and calculate a single net amount owed, rather than fighting each trade individually.
The Credit Support Annex, or CSA, sits alongside the master agreement and governs collateral. It specifies what collateral is acceptable, how often it is recalculated, and the thresholds that trigger collateral calls. For uncleared basis swaps, the CSA is where the practical details of margin posting get worked out between the parties.
Risks to Watch
Basis risk is the obvious one, and it cuts both ways. The swap is meant to hedge basis risk, but if the spread moves in a direction the institution did not anticipate, the swap itself generates losses. A hedge that offsets today’s mismatch is still exposed to the chance that the mismatch shifts in character over time.
Counterparty credit risk is the more dangerous concern for uncleared trades. If the party on the other side defaults when the swap has significant positive value to you, recovering that value becomes a collections problem. Collateral posted under a CSA mitigates the exposure, and central clearing largely eliminates it for cleared swaps. For bilateral, uncleared basis swaps between institutions that do not post full collateral, counterparty risk can be substantial.
Mark-to-market risk matters even if you intend to hold the swap to maturity. As market conditions change, the fair value of the swap moves, and those swings flow through the balance sheet. On a $500 million notional, even small shifts in the expected spread can produce multi-million-dollar changes in reported value. That can prompt margin calls on uncleared swaps and affect capital ratios for regulated institutions.
Liquidity risk is the quietest threat. Basis swap markets are less liquid than plain-vanilla interest rate swap markets. Exiting early means finding a counterparty willing to take the other side, and the bid-ask spread on that unwind can be costly. During market stress, when basis spreads move fastest and the need to adjust positions is greatest, liquidity tends to evaporate.