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Chapter 8. Inflation-Linked Bonds

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Chapter 8. Inflation-Linked Bonds

Inflation is the silent erosion of wealth. A bond paying 3% annual coupon sounds attractive until inflation runs 4%, leaving you with negative 1% real return. Inflation-linked bonds solve this problem by adjusting both principal and coupon payments to track official inflation indices, ensuring that your purchasing power grows (or at least doesn't shrink) even as the cost of living rises.

The three largest inflation-linked bond markets serve different regions and use different inflation measures. US Treasury Inflation-Protected Securities (TIPS) track the Consumer Price Index (CPI) and represent the largest, most liquid market globally. UK index-linked gilts link to the Retail Price Index (RPI), which includes housing costs and runs slightly higher than CPI, making them favored by UK pension funds paying inflation-linked pensions. French OAT-i and other Eurozone linkers track the Harmonized Index of Consumer Prices excluding tobacco (HICP ex-tobacco), operating in a low-inflation environment shaped by ECB policy.

All inflation-linked bonds share a core feature: principal is multiplied by an inflation ratio (current inflation index divided by the reference index at issuance), and coupons are paid on the inflation-adjusted principal. A £100,000 gilt with a 2% coupon and 3% cumulative inflation has an adjusted principal of £103,000 and delivers a £2,060 coupon payment (2% of £103,000), not £2,000. Over decades, this dual compounding of inflation adjustment into coupon payments is why inflation-linked bonds deliver inflation-matching returns.

The trade-off is real yield. A traditional bond might offer 4% coupon; an inflation-linked alternative offers 1% coupon because the inflation adjustment is the investor's real return. This means inflation-linked bonds underperform when inflation undershoots expectations (your real yield was locked in too low) and outperform when inflation exceeds expectations (the principal adjustment yields unexpected wealth). They are bets on inflation being higher than the market has priced in, with the added benefit of certainty around purchasing power if inflation surprises occur.

For investors with long time horizons and explicit inflation-linked liabilities (pension funds paying inflation-adjusted pensions, endowments spending inflation-adjusted amounts), inflation-linked bonds are essential. For retail investors, the decision hinges on inflation expectations versus consensus and tolerance for negative real yields in low-inflation environments. An allocation to inflation-linked bonds—say 25% of a 50% total bond portfolio, or 12.5% of overall assets—provides meaningful inflation protection without overcommitting to a single inflation forecast.

Taxation complicates US TIPS: phantom income (the annual principal adjustment) is taxed as ordinary income even though you don't receive the cash, creating brutal tax bills in taxable accounts. High-income investors often hold TIPS only in tax-deferred retirement accounts (401k, IRA) where phantom income is not taxed annually. Series I Savings Bonds, a non-marketable alternative, defer taxation until redemption, making them more tax-efficient for taxable investors, but they have strict purchase limits and liquidity constraints.

Understanding the mechanics of each market—TIPS' three-month lag in CPI adjustments, UK gilts' in-arrears adjustments with eight-month lags, and Eurozone linkers' persistent negative real yields—equips you to make thoughtful allocation decisions and avoid surprises when holding these bonds through economic cycles.

What's in this chapter​

How to read it​

Start with "What Inflation-Linked Bonds Are" to understand the core mechanics of principal indexation and why these bonds exist. Then proceed through "Real Yield vs Nominal Yield" to grasp the inflation-expectation trade-offs inherent in all inflation-linked investing.

For US investors, the three articles on TIPS mechanics ("TIPS Mechanics," "TIPS CPI Adjustment," "TIPS Tax Treatment and Phantom Income") are essential. Read them in sequence to understand how principal adjusts, why the three-month lag matters, and why phantom income is a tax trap in high-bracket taxable accounts.

International investors should read "UK Index-Linked Gilts" and "French OAT-i and Eurozone Linkers" to understand regional market dynamics and why real yields differ across markets. These articles clarify currency risk and institutional demand effects.

"Deflation Floor Protection" is a critical article for understanding what happens in rare deflation scenarios. It's not required reading for investors primarily focused on inflation hedging, but it clarifies the insurance value embedded in all inflation-linked bonds.

Finally, "TIPS vs I Bonds" compares the two main inflation-linked vehicles available to US retail investors and guides you to the right choice based on account type, time horizon, and allocation size.

A practitioner reading this chapter straight through will build a holistic understanding of global inflation-linked bond markets. Someone seeking answers to specific questions (How do TIPS work? Should I hold inflation-linked bonds in my IRA?) can jump to the relevant article.