What drives swap spreads and what does a negative swap spread mean?

Swap spreads are a fascinating topic that connects derivatives, fixed income, and macroeconomics. Let's break it down.

What is a Swap Spread?

Swap spread = Fixed rate on an interest rate swap − Yield on a matching-maturity Treasury bond

For example, if the 10-year swap rate is 4.35% and the 10-year Treasury yield is 4.10%, the 10-year swap spread is 25 basis points.

Why Should Swap Spreads Be Positive?

In an interest rate swap, you're exchanging fixed payments for SOFR-based floating payments with a counterparty (typically a bank). Since bank counterparties carry some credit risk (unlike Treasuries), the fixed swap rate should exceed the Treasury yield — hence a positive spread.

What Drives Swap Spreads?

1. Credit risk perception — When bank creditworthiness deteriorates, swap spreads widen.
2. Supply of Treasuries — Heavy Treasury issuance pushes Treasury yields up, compressing swap spreads.
3. Balance sheet constraints — Post-2008 regulations (Basel III, Dodd-Frank) limit dealers' balance sheets, affecting their ability to arbitrage swap spread dislocations.
4. Hedging demand — Corporate bond issuers who swap fixed to floating increase demand for receiving fixed, pushing swap rates down.

The Negative Swap Spread Puzzle

In the US, 30-year swap spreads turned negative around 2015 and have stayed there intermittently. This seems paradoxical — why would a swap with credit risk yield less than a 'risk-free' Treasury?

Explanation:

• Massive Treasury supply (federal deficits) pushes long-end Treasury yields higher
• Post-crisis regulation makes it expensive for dealers to hold Treasuries on balance sheet
• Heavy demand from pension funds and insurers to receive fixed on long-dated swaps pushes swap rates down
• The net effect: Treasuries become relatively more expensive to hold than swaps, so the spread inverts

Practical Significance:

A portfolio manager at Northcrest Advisors uses swap spreads as a macro signal:

• Widening swap spreads → Rising credit concerns, potential stress in banking sector
• Narrowing/negative swap spreads → Supply-demand imbalance in Treasuries, regulatory constraints

CFA Exam Tip: If a question asks 'which factor most likely explains negative 30-year swap spreads,' look for answers mentioning Treasury supply or regulatory balance sheet constraints — not credit risk (which would push spreads wider, not negative).

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