Inflation-linked bonds: how TIPS and linkers protect purchasing power

Inflation-linked bonds are government bonds whose principal—and therefore coupon payments—adjust automatically with inflation. Unlike nominal bonds, which pay a fixed coupon on a fixed principal, inflation-linked bonds protect the real value of capital: if inflation runs at 3% per year, the bond's principal grows by 3% per year, and so does the coupon payment. The investor is guaranteed a real return above inflation rather than a nominal return that inflation erodes.

What inflation-linked bonds are

The most widely held inflation-linked bonds are US Treasury Inflation-Protected Securities (TIPS) and UK index-linked gilts (linkers). Similar instruments exist in most major bond markets: France issues OATi and OATei bonds, Germany issues Bundesobligationen (Bund-i), and Japan issues JGBi. All follow the same basic structure: the principal adjusts with a reference inflation index—typically the Consumer Price Index (CPI)—and the coupon is paid as a fixed percentage of the inflation-adjusted principal.

The real yield is the yield to maturity on an inflation-linked bond. It represents the annual return above inflation that the investor will receive if they hold the bond to maturity and all payments are made as promised. When a ten-year TIPS has a real yield of 1.5%, the investor will earn 1.5% per year above the rate of inflation over the ten-year period. This contrasts with a nominal ten-year Treasury: if the nominal bond yields 4.5% and inflation averages 3%, the real return is approximately 1.5%—but the investor bears the risk that inflation turns out to be higher or lower than expected.

How it works

The inflation adjustment mechanism is transparent. For TIPS, the principal is adjusted daily based on the non-seasonally adjusted CPI for Urban Consumers (CPI-U), with a three-month lag. A TIPS issued at a principal of USD 1,000 with a coupon of 0.5% per year will, after one year of 3% inflation, have an adjusted principal of USD 1,030—and the coupon payment will be USD 5.15 (0.5% of USD 1,030) rather than USD 5.00. At maturity, the investor receives the inflation-adjusted principal, with a guarantee that it will not fall below the original principal in the event of deflation.

Real yields are related to nominal yields through the Fisher equation: nominal yield ≈ real yield + expected inflation. When nominal yields are 4.5% and TIPS real yields are 1.5%, the implied break-even inflation rate is 3%—the level of inflation at which a nominal bond and an inflation-linked bond produce the same return. If actual inflation turns out to be higher than 3%, the TIPS outperforms the nominal bond; if lower than 3%, the nominal bond outperforms. The break-even rate is the market's implied forecast of average inflation over the bond's life.

What the evidence shows

Inflation-linked bonds have historically provided effective inflation protection over holding periods comparable to their duration. Research on TIPS performance covering 1997–2022 found that TIPS reliably tracked realised inflation over five-year and ten-year periods, delivering real returns close to their starting real yields. The protection was most valuable during the 2021–2022 inflation surge: TIPS significantly outperformed nominal Treasuries of similar maturity as inflation expectations rose sharply.

Real yields can be negative—a condition that occurred frequently in the 2010s and early 2020s when central bank asset purchase programmes drove nominal bond prices up and real yields below zero. A negative real yield means the investor is paying, in real terms, for the certainty of inflation protection. Whether this is rational depends on the investor's inflation risk aversion and the alternatives available.

Limitations and trade-offs

Inflation-linked bonds protect against measured consumer price inflation, but the index may not perfectly match the inflation experienced by a specific investor. An investor whose costs are dominated by healthcare or education—categories that have historically inflated faster than the CPI—will find that TIPS provide only partial protection. The three-month lag in the inflation adjustment also means that very recent inflation surges are not immediately reflected in the principal adjustment.

TIPS are subject to the same interest rate risk as nominal bonds: if real yields rise, TIPS prices fall, and the investor can experience mark-to-market losses even though the inflation protection mechanism remains intact. During the 2022 rate surge, long-duration TIPS fell substantially in price as real yields rose sharply from negative to positive, despite the concurrent high inflation environment.

Inflation-linked bonds in pfolio

Inflation-linked bond ETFs are part of pfolio's fixed income universe and can serve as an inflation hedge within a diversified portfolio. They are particularly relevant for investors who are concerned about long-run inflation eroding the purchasing power of their wealth. Available inflation-linked bond ETFs are listed in the Assets section. For context on the role of inflation in portfolio returns more broadly, see inflation and portfolio returns. Fixed income performance is tracked in pfolio Insights.

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