How does cash flow matching work in liability-driven investing, and when is it preferred over duration matching?

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AcadiFi · Accepted Answer

Cash flow matching (also called "dedication") is the most conservative form of liability-driven investing, eliminating reinvestment risk by matching each liability payment with a corresponding bond cash flow. **How Cash Flow Matching Works** The portfolio is constructed so that bond coupons and principal repayments **exactly coincide** in timing and amount with each future liability payment. The process works backward from the last liability. **Worked Example — Evergreen Pension Fund:** Evergreen has fixed pension obligations over the next 5 years: | Year | Liability Payment | |---|---| | 1 | $8,000,000 | | 2 | $8,500,000 | | 3 | $9,000,000 | | 4 | $7,500,000 | | 5 | $12,000,000 (final + large cohort retiring) | **Step-by-step Dedication (Working Backward):** **Year 5:** Buy a 5-year zero-coupon bond maturing at $12,000,000. Cost at 4% yield: $12M / (1.04)^5 = $9,863,000. **Year 4:** Buy a 4-year zero-coupon bond maturing at $7,500,000. Cost at 3.8%: $7.5M / (1.038)^4 = $6,465,000. **Year 3:** Buy a 3-year zero-coupon bond maturing at $9,000,000. Cost at 3.6%: $9M / (1.036)^3 = $7,998,000. **Year 2:** Buy a 2-year zero-coupon bond maturing at $8,500,000. Cost at 3.4%: $8.5M / (1.034)^2 = $7,949,000. **Year 1:** Buy a 1-year zero-coupon bond maturing at $8,000,000. Cost at 3.2%: $8M / (1.032) = $7,752,000. | Year | Bond Face Value | Cost Today | Liability Met? | |---|---|---|---| | 1 | $8,000,000 | $7,752,000 | Yes | | 2 | $8,500,000 | $7,949,000 | Yes | | 3 | $9,000,000 | $7,998,000 | Yes | | 4 | $7,500,000 | $6,465,000 | Yes | | 5 | $12,000,000 | $9,863,000 | Yes | | **Total cost** | | **$40,027,000** | | \`\`\`mermaid flowchart TD A["Identify All
Future Liabilities"] --> B["Start From
Last Liability"] B --> C["Buy Bond Maturing
at Liability Date"] C --> D["Work Backward
to Next Liability"] D --> E{"More Liabilities?"} E -->|"Yes"| C E -->|"No"| F["Portfolio Complete:
All Liabilities Matched"] F --> G["No Reinvestment Risk
No Interest Rate Risk"] \`\`\` **Cash Flow Matching vs. Duration Matching:** | Feature | Cash Flow Matching | Duration Matching | |---|---|---| | Reinvestment risk | **Eliminated** | Present (requires rebalancing) | | Interest rate risk | **Eliminated** (if held to maturity) | Hedged only for parallel shifts | | Cost | Higher (restrictive constraints) | Lower (more flexibility) | | Rebalancing | None needed | Periodic rebalancing required | | Complexity | Simple concept, hard to execute perfectly | Moderate concept, easier execution | | Asset universe | Limited to bonds with matching maturities | Broader universe acceptable | | Surplus management | No surplus optimization | Can optimize surplus return | **When to Use Cash Flow Matching:** 1. **Regulatory requirements** demand absolute certainty of meeting obligations. 2. **Short time horizons** where duration matching approximation errors accumulate. 3. **Liability stream is fixed and known** with certainty (no inflation indexing, no optionality). 4. **Conservative mandates** where the cost of a shortfall far exceeds the cost of holding a suboptimal portfolio. **Practical Challenges:** - Exact maturity matches may not exist in the bond market. - Using coupon bonds creates intermediate cash flows that must be reinvested or pre-allocated. - The approach is more expensive because it constrains the portfolio significantly. - Real-world liabilities often have uncertain timing and amounts (unlike our clean example). See our CFA Level II Portfolio Management course for LDI strategies.

How does cash flow matching work in liability-driven investing, and when is it preferred over duration matching?

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