A basis swap is a contract between two parties to exchange streams of floating interest payments, with each stream tied to a different floating-rate benchmark. Both legs float, which sets it apart from a standard interest rate swap where one leg is fixed. The notional principal used to size the payments is never exchanged; it exists only as a reference figure for the interest calculations. Banks, insurers, large corporate treasuries, and other institutional players use these contracts to manage the risk that two floating benchmarks will drift apart in ways that hurt their balance sheets.
How It Differs From a Standard Interest Rate Swap
In a plain-vanilla interest rate swap, one party pays a fixed rate and the other pays a floating rate. A basis swap replaces the fixed leg with a second floating leg pegged to a different benchmark. The gap between those two benchmarks is the “basis,” and that gap is the entire point of the trade.
The two benchmarks can be different indices altogether, such as the federal funds rate against the prime rate. They can also be different tenors of the same index, like 3-month SOFR against 6-month SOFR. Either way, the parties are hedging or speculating on the relationship between the two rates, not the direction of interest rates overall.
Because the notional is never exchanged, a $500 million basis swap does not involve $500 million moving between the counterparties. That figure only scales the interest math to match the real exposure being hedged.
How the Payments Are Calculated
Every basis swap has three moving parts: the two floating indices, the notional principal, and a fixed spread added to one leg. The spread is calibrated so that the present value of the expected cash flows on both sides is equal at the moment the contract starts, a condition known as zero net present value at inception. Without it, one party would be structurally ahead from day one.
On each payment date, both sides work out what they owe by multiplying their respective rate by the notional and the fraction of the year covered. Suppose Party A pays based on 3-month SOFR and Party B pays based on 6-month SOFR plus 5 basis points. The CME Group publishes forward-looking Term SOFR reference rates for 1-month, 3-month, 6-month, and 12-month tenors, giving both parties a standardized input for those calculations.
Only the net difference actually changes hands. If Party A’s obligation comes to $1.5 million and Party B’s comes to $1.4 million, Party A sends $100,000 to Party B. 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. That netting cuts settlement risk considerably.
Payment frequency is usually quarterly or semi-annual, set in the swap agreement. The notional itself can also change over time. An amortizing swap has a notional that declines on a schedule, which fits when hedging a loan portfolio that pays down over its life. An accreting swap grows the notional to match exposures that build up. The mechanics stay the same; only the size of each period’s cash flows changes.
The Three Main Types
Basis swaps generally fall into three categories, each addressing a different kind of mismatch.
Index-to-Index Swaps
These exchange payments tied to two entirely different benchmarks. A bank might swap federal funds exposure for prime rate exposure, or trade SOFR-based payments against payments tied to a different overnight rate. The two indices usually cover different parts of the money market with different credit and liquidity characteristics, and the swap lets institutions align their funding costs with lending revenues priced off different benchmarks.
Tenor Swaps
Tenor swaps use the same underlying index at different reset periods. Swapping 3-month SOFR for 6-month SOFR is the standard example. Both rates come from the same overnight secured funding market, but they price differently because the longer tenor carries more term risk and different liquidity assumptions. A bank whose assets reset every six months while its liabilities reset every three months can close that gap with a tenor swap.
Cross-Currency Basis Swaps
These exchange floating rates in different currencies, such as SOFR-based dollar payments against euro payments tied to €STR. The Bank for International Settlements describes the basic 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 basis swaps, cross-currency versions usually involve an actual exchange of principal at the start and end of the contract, because the parties want the foreign currency itself, not just the rate exposure.
Why Institutions Enter Basis Swaps
The main use case is managing an asset-liability mismatch. 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 move together most of the time, but not perfectly. When the funding rate climbs faster than the lending rate, net interest margin compresses. That is basis risk, and it can quietly eat into earnings even when overall interest rates hold steady.
The bank fixes this by entering a basis swap in which it pays federal funds and receives prime on a $500 million notional. If funding costs spike relative to loan income, the swap pays the difference. If the spread moves the other way, the bank pays into the swap but earns more on its loan book. Net interest margin stays predictable either way.
This kind of structural hedging is the standard use for basis swaps. Banks, insurance companies, and corporate treasuries with complex balance sheets use them to lock in spreads that would otherwise float around. The alternative is accepting that profitability depends on two benchmarks staying in a stable relationship, which history suggests is a poor bet over multi-year horizons.
Traders also use basis swaps tactically. Someone who thinks SOFR will tighten relative to fed funds can enter a basis swap that profits from that convergence without taking a directional bet on rates themselves.
What Moves the Basis Spread
The fixed spread added to one leg is not arbitrary. It reflects several factors, and it 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 commands a tighter spread than one tied to a thinner market. The party taking exposure to the less liquid index 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 visible: LIBOR embedded the credit risk of the interbank lending market, while SOFR is a nearly risk-free rate backed by Treasury collateral. A swap between a credit-sensitive rate and a risk-free rate needs a spread that reflects that fundamental gap. The discontinuation of the Bloomberg Short-Term Bank Yield Index (BSBY) on November 15, 2024 narrowed the menu of credit-sensitive alternatives, pushing more activity toward SOFR-based instruments and reshaping basis swap pricing.
Supply and demand imbalances also push spreads around. When many institutions want to receive one index and pay the other at the same time, the spread adjusts. Regulatory changes amplify this: new capital requirements or changes in how regulators treat certain exposures can suddenly make one side of a basis swap more expensive.
Central bank policy expectations feed in as well. If the market anticipates a shift in monetary policy that will affect the two indices differently, the spread reprices quickly to reflect that view.
Regulatory and Documentation Framework
Basis swaps are over-the-counter derivatives, and the rules governing them changed substantially after 2008. The Dodd-Frank Act brought in mandatory clearing for standardized contracts, mandatory reporting, and margin requirements for uncleared trades.
The Commodity Futures Trading Commission requires certain interest rate swap classes to clear through registered derivatives clearing organizations, and that 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 benchmarks in other currencies, such as EURIBOR-based basis swaps in euros, also fall under the clearing mandate. Central clearing inserts a clearinghouse between the two parties, who then post collateral daily, cutting counterparty credit risk. Highly customized structures with non-standard terms usually stay bilateral.
All swaps, cleared or not, must be reported to a swap data repository. Uncleared basis swaps are subject to both initial and variation margin requirements. Under CFTC rules, initial margin requirements apply to entities whose average month-end aggregate notional amount of uncleared swaps exceeds $8 billion, calculated using the March, April, and May figures of the relevant year. Variation margin applies more broadly.
On the contract itself, nearly every institutional basis swap is governed by an ISDA Master Agreement. The 2002 version includes provisions for measuring damages on default, force majeure, set-off rights, and close-out netting, which lets a non-defaulting party terminate all outstanding transactions and calculate a single net amount owed. The Credit Support Annex sits alongside the master agreement and covers collateral: what qualifies, how often it is recalculated, and the thresholds that trigger collateral calls.
Risks to Understand
Basis risk itself cuts both ways. A basis swap is designed to hedge that risk, but if the spread between the two indices moves against the institution, the swap generates losses. A hedge that offsets today’s mismatch is still exposed to the mismatch changing shape over time.
Counterparty credit risk is the sharper concern on uncleared swaps. If the other party defaults when the swap has significant positive value, collecting that value becomes a workout problem. Collateral posted under a CSA mitigates this, and central clearing largely removes it for cleared trades. For bilateral swaps between institutions that do not post full collateral, counterparty risk can be substantial.
Mark-to-market risk matters even when the plan is to hold the swap to maturity. Fair value moves with market conditions and flows through the balance sheet. On a $500 million notional, even small changes in the expected spread can produce multi-million-dollar swings in reported value, which can trigger margin calls on uncleared swaps and affect capital ratios for regulated institutions.
Liquidity risk is the quietest threat. Basis swap markets are thinner than the plain-vanilla interest rate swap market. Exiting a position before maturity 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 spreads move fastest and the urge to adjust positions is greatest, that liquidity tends to disappear.