Using Interest Rate Swaps in Bond Portfolios

Interest rate swaps are the workhorse derivative for institutional bond managers. A pension fund that needs 15-year duration to match liabilities but can only source 7-year corporates at attractive spreads faces a structural problem. The swap market solves it: receive fixed on a 10-year swap, and the portfolio's effective duration extends without selling a single bond. The mechanics matter less than understanding why this trade dominates fixed income hedging (the swap market traded $311.9 trillion in notional through September 2024, per ISDA data).

The point is: swaps let managers separate their credit views from their rate views. You can own the corporate bond for its spread and hedge away the rate risk entirely, or you can amplify duration beyond what cash bonds allow.

Swap Mechanics (Why the Structure Matters)

A plain-vanilla interest rate swap involves two parties exchanging cash flows: one pays a fixed rate, the other pays a floating rate (now typically SOFR, replacing LIBOR post-2021 transition). At inception, the present value of fixed payments equals the expected present value of floating payments. No cash changes hands at the start (Kolb & Overdahl, 2007).

Why this matters: A manager receiving fixed gains when rates fall (the fixed payments become more valuable relative to declining floating rates) and loses when rates rise. Receiving fixed adds duration. Paying fixed removes duration.

The math is straightforward but the implications profound:

• Portfolio duration = 4 years, benchmark duration = 6 years
• Solution: Enter a receive-fixed swap with duration contribution of +2 years
• Result: Portfolio now tracks benchmark duration without buying long bonds

The swap curve (yields implied by swap fixed rates) has increasingly supplanted Treasury yields as the discount curve for corporate bonds. PIMCO notes this shift reflects bank credit embedded in swap rates and SOFR expectations (PIMCO, 2024). When you price a corporate bond, you're often discounting off swaps, not Treasuries.

Cleared vs. Bilateral: The Post-2008 Regime

Lehman Brothers' collapse crystallized counterparty risk in OTC derivatives. The firm had 906,000 derivative transactions under 6,120 ISDA Master Agreements with an estimated $35 trillion notional. Settlement took years across 80+ jurisdictions (IMF, 2008). The response was mandatory central clearing.

The durable lesson: Clearinghouses don't eliminate risk; they transform bilateral credit exposure into standardized margin requirements.

Today, 81.7% of interest rate derivative transactions clear through central counterparties like LCH or CME. For fixed-for-floating swaps specifically, 90.6% are cleared (ISDA, Q3 2024). The remaining bilateral trades (typically bespoke structures or smaller counterparties) still require ISDA documentation, credit support annexes (CSAs), and regular margin posting.

Clearing mechanics for bond managers:

• Initial margin: Typically 1-5% of notional, posted upfront
• Variation margin: Daily cash settlements based on mark-to-market moves
• Portability: If your clearing member fails, positions can transfer to another member

The 2022 UK LDI crisis demonstrated what happens when margin calls cascade. Gilt yields rose 100+ bps in four days following the Kwarteng mini-budget. Pension funds using leveraged swap positions faced 25 billion GBP in forced gilt sales over five weeks to meet variation margin (Bank of England, 2022). Pre-crisis, managers maintained ~150 bps yield headroom. Post-crisis, the Financial Policy Committee recommends 250-300 bps minimum (FPC, 2023).

Practical Applications in Portfolio Construction

Duration Extension Without Cash Outlay

A $500 million core-plus fund holds investment-grade corporates with 5.2-year duration against a 6.5-year benchmark. Buying long bonds would work but sacrifices the attractive spreads in 5-7 year maturities. Instead:

• Trade: Enter $200 million notional 10-year receive-fixed swap (duration contribution ~8.5 years on notional)
• Duration added: (200/500) x 8.5 = 3.4 years
• New portfolio duration: 5.2 + 3.4 = 8.6 years (overshoot adjustable via notional sizing)

The portfolio maintains its credit positioning while achieving duration targets. Cost? Margin requirements and the spread between the fixed rate and where floating settles. No bonds sold, no transaction costs on the cash portfolio.

Hedging Rate Risk on Corporate Holdings

The opposite application: a high-yield manager bullish on spreads but nervous about rising rates. The portfolio holds $300 million in BB-rated credits with 4.5-year duration.

• Trade: Enter $300 million notional 5-year pay-fixed swap
• Duration removed: Portfolio effective duration approaches zero on rate moves
• Spread exposure: Fully retained (swaps don't hedge credit risk)

The test: If rates rise 100 bps and spreads unchanged, the cash bonds lose ~4.5% but the swap gains ~4.5%. If spreads widen 100 bps with rates flat, you absorb the full credit loss. The swap isolates the bet you want to make.

Curve Positioning with Swap Combinations

Managers with yield curve views can combine swaps at different tenors. Expecting curve steepening (long rates rising faster than short)?

• Pay fixed on 10-year swap (loses if long rates fall, gains if they rise)
• Receive fixed on 2-year swap (gains if short rates fall relative to long)

This "steepener" trade profits from the spread between 10s and 2s widening, regardless of the absolute rate level. Notional amounts adjust for relative durations: a 10-year swap has ~5x the duration sensitivity of a 2-year, so a duration-neutral steepener uses roughly 5:1 notional ratio (short:long).

Risk Management Essentials

Counterparty exposure (even when cleared): Your clearing member is your immediate counterparty. If they fail before margin transfers, you're exposed. Diversifying clearing relationships mitigates this tail risk.

Basis risk: The swap curve and Treasury curve don't move in lockstep. A hedge using swaps against Treasury exposure can underperform if the swap spread (difference between swap rate and Treasury yield at same maturity) moves against you. In March 2020, swap spreads widened sharply during the Treasury market stress (NY Fed, 2020).

Roll risk: Most institutional swaps are multi-year, but short-dated swaps (under 2 years) may need rolling. Each roll resets the fixed rate to prevailing market levels, potentially at worse terms.

Operational overhead: Daily margin calculations, collateral management (posting eligible securities or cash), and maintaining clearing member relationships require back-office infrastructure that smaller managers may lack.

When Swaps Outperform Alternatives

Treasury futures remain valuable for smaller adjustments and standardized exposures. But swaps offer tenor customization (any maturity, not just quarterly contract cycles) and avoid the basis risk between futures prices and underlying cheapest-to-deliver bonds.

Checklist: Implementing Swaps in Your Portfolio

Essential (Do These First)

• Establish ISDA Master Agreement and CSA with at least one dealer
• Secure clearing membership (direct or through FCM relationship)
• Model margin requirements under stress scenarios (250+ bps yield shock)
• Define maximum swap notional relative to portfolio AUM (leverage limits)

High-Impact Refinements

• Monitor swap spread levels versus historical ranges before hedging
• Implement daily P&L attribution separating swap and cash bond contributions
• Stress test combined portfolio (cash + swaps) for basis risk scenarios

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The bottom line: Interest rate swaps transform duration from a constraint into a choice. A $300 million portfolio can behave like a $500 million portfolio in duration terms, or hedge away rate risk entirely while keeping credit exposure. The 2022 LDI crisis proved the risks of leverage without liquidity buffers, but the tool itself remains essential. The question isn't whether to use swaps; it's whether you've sized the margin buffer for the tail event that always seems impossible until it happens.

Citation: Kolb, R. & Overdahl, J. (2007). Futures, Options, and Swaps. Blackwell Publishing.