What Is a Basis Swap?
Michael Whitman
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Trading since 2017, full-time since 2020
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YouTube creator, 137K subscribers
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Published 2026-09-14
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Updated
Basis swap is an interest rate swap in which both legs are floating, referencing different rates or different tenors of the same rate. It exists to manage the spread between two rates that are expected to track each other, and that spread is itself a traded price.
A normal swap exchanges fixed for floating. A basis swap exchanges floating for floating — which sounds pointless until you notice that two floating rates are not the same rate.
How it works
Both legs reference a floating rate, but different ones — different benchmarks, different currencies, or the same benchmark at different tenors.
One leg carries a spread. Since the two rates are not identical in value, a fixed adjustment is added to one side to make the swap worth zero at the start.
That spread is the traded price. It moves, it is quoted, and it is the entire economic content of the instrument.
Netting shrank dealers’ exposure to $3.35 trillion at end-2025, 14.70% of gross market value, a fall from 46.95% in 1998, per counterparty credit risk.
Swaps that pass along an asset’s whole return price their funding leg the same way, as a spread over a floating rate; the total return swap page found TQQQ paying Fed funds plus 0.85% to 1.30% in May 2026.
Why two floating rates differ at all
Different credit content. A rate reflecting unsecured bank lending carries bank credit risk; one reflecting secured overnight lending does not, and the gap between them is a price for that difference.
Different tenors. Three-month money and one-month money are not interchangeable; borrowing for longer carries more of whatever the market is worried about.
And different currencies. A cross-currency basis reflects relative demand for funding in each currency, and it can move sharply when one becomes hard to obtain.
A worked example
A bank’s assets earn three-month floating. Its liabilities cost one-month floating, because that is how its depositors and funding markets work.
Those two rates normally move together — but not identically, and the difference between them is the bank’s margin moving around for reasons unconnected to its lending decisions.
A basis swap exchanges one for the other, locking the relationship and leaving the bank with a stable margin.
What it has bought is not protection against rates moving. Both legs float, so a general rise or fall passes through both sides. It has bought protection against the two rates moving differently, which is a much narrower and much less obvious risk.
When the spread stops being boring
In calm conditions it is a few basis points and nobody looks. The two rates track, the swap is uneventful, and the instrument is pure plumbing.
In funding stress it moves violently. A widening cross-currency basis means institutions are paying a premium to obtain one currency, which is a direct measure of scarcity rather than an opinion about it.
Which makes the basis a diagnostic. It is one of the few prices that reflects the mechanics of funding rather than views about the economy, and it moves before most sentiment measures do.
And it is why these instruments get attention in crises and none the rest of the time. The quantity being traded is the assumption that two similar things stay similar, and that assumption is exactly what breaks first when a system is under strain.
The original data
The S&P 500’s worst fall since 1950 took it 56.8% below its record, from a close of 1565.15 on 9 Oct 2007 to 676.53 on 9 Mar 2009.
That tail, not the everyday wobble, is the relevant shape here. A basis spread behaves the same way — negligible almost always, and capable of a move many times its typical size in conditions that are rare and not absent.
And the index’s own history makes the same point about persistence: it closed below a prior record on 93% of trading days, and the longest wait for a new one ran from January 1973 to July 1980. A dislocated basis can stay dislocated far longer than a position sized for the calm case can survive.
Who uses them
Banks managing asset and liability mismatches, which is the largest use by volume and the least visible.
Corporates with debt in one currency and revenue in another, where the cross-currency basis is a real cost of running the business.
And relative-value traders taking a view on the spread itself, which is a position that looks safe because both legs float, and is not.
That last group is where the instrument earns its reputation. A basis position appears hedged — no outright rate exposure, no direction — and what remains is a leveraged bet on two things staying related, which is the shape of position that has historically produced the most surprising losses.
And banks themselves, structurally. A bank borrows short and lends long as a matter of business model, so a basis exposure is not a position it chose but a by-product of existing at all — which is why this market’s largest participants are also its most consistent users.
How this connects
Its fixed-rate relative is the forward rate agreement. That contract locks one future floating rate against a fixed one; a basis swap never fixes anything and only locks the gap between two floating rates.
Tenor basis sits alongside the yield curve. When longer money costs more than the curve’s slope alone explains, the extra is a premium for lending term, and a tenor basis swap prices exactly that premium.
A widening basis is a reading of funding liquidity risk, the danger that an institution cannot roll its borrowing, as distinct from the risk that an asset cannot be sold.
Secured overnight rates are backed by government debt, which is why they trade close to the treasury bill rate and why the bond market effectively sets the level of that leg.
Exchange rate risk is handled by the structure. A cross-currency basis swap exchanges principal at the start and the end as well as interest, so the currency is covered and the funding premium is what remains.
Like any over-the-counter contract it carries counterparty risk, and the stress that widens the spread is the same stress that weakens the other side.
And the relative-value trade is usually run with leverage, because a spread that barely moves in calm conditions earns almost nothing unless the notional is large.
When it fails
The characteristic failure is treating a narrow spread as a stable one. A basis that has sat within a few basis points for years looks like a low-risk carry opportunity, and the position is sized against that history. The history describes calm conditions, the spread is a measure of funding stress, and it moves by a multiple of its normal range precisely when everything else is also going wrong. The risk was not absent; it was dormant, and a long quiet period made it look smaller rather than making it smaller.
A second failure is calling a floating-floating position hedged. It has no outright rate exposure and a large exposure to the relationship.
A third is ignoring the credit content of a reference rate, which is what most of the spread is actually paying for.
A fourth is assuming benchmark reform left old relationships intact. The replacement of legacy benchmarks changed the credit content of several rates, and the bases between them changed with it.
The question: The spread tripled. Add or exit?
And a fifth is not watching it. For most people a basis is not a position to take, and it is one of the better free indicators of funding conditions available.
Related
Interest rate swap covers the fixed-for-floating version. Basis risk covers the general problem of a hedge that does not track. And constant maturity swap covers another variation on the floating leg.
A basis swap trades the gap between two things that are supposed to be the same. Those gaps are usually tiny and boring, and when they stop being tiny it is nearly always because something in the funding system has gone wrong.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.