What Inflation-Linked Bonds Are
What Inflation-Linked Bonds Are
Inflation-linked bonds adjust their principal and coupon payments to track inflation, ensuring your real purchasing power is preserved even as the cost of living rises.
Key takeaways
- Principal of inflation-linked bonds rises or falls directly with inflation indices (CPI, RPI, HICP)
- Coupon payments are calculated on the inflation-adjusted principal, multiplying the inflation effect
- Unlike traditional bonds, they protect against inflation erosion—the silent wealth destroyer
- Three main regional variants dominate: US TIPS, UK index-linked gilts, and French OAT-i bonds
- A modest real yield (0–2% annually) is the price for inflation protection and capital preservation
The erosion problem traditional bonds cannot solve
When you buy a regular bond paying 3% annual coupon, you think you're earning 3%. But if inflation runs at 4% that year, you're actually losing 1% in real purchasing power. After 10 years of 3% inflation, a £100,000 nest egg buys what £74,000 bought before. Most savers never calculate this loss. Central banks pump inflation into the economy, asset prices rise, necessities cost more, and yet bond investors who held nominal bonds through the 1970s saw their real returns turn negative.
Inflation-linked bonds solve this directly. Instead of paying a fixed coupon, they index both principal and coupon to official inflation measures. If inflation rises, so does every future payment. If deflation occurs (rare but possible), principal doesn't fall below par under standard designs. The trade-off is real: you accept a lower nominal coupon—often 0.5% to 2% instead of 3% to 5%—because the inflation adjustment is your real return.
How principal indexation works
An inflation-linked bond issued at £1,000 par with a 1% coupon doesn't pay you £10 annually. Instead, the principal adjusts monthly or semi-annually based on the official inflation index. If inflation that month was 0.25%, your principal becomes £1,002.50, and your 1% coupon is calculated on that new amount, giving you £10.03.
Over a 10-year holding period with average 2% annual inflation, your original £1,000 principal grows to about £1,219. Your coupon payments—all calculated on progressively larger principal amounts—compound the inflation adjustment. This dual indexation (principal + coupon) is why inflation-linked bonds can deliver real returns even at seemingly low nominal coupons.
The three main types
US Treasury Inflation-Protected Securities (TIPS) are the largest and most liquid inflation-linked market globally. They track the Consumer Price Index (CPI) and trade on the secondary market like any Treasury bond. A 10-year TIPS issued at £100,000 with a 1.5% coupon will adjust monthly based on CPI, and both principal and interest are taxed differently in the US, creating the famous "phantom income" issue.
UK Index-Linked Gilts link to the Retail Price Index (RPI), which includes housing costs and tends to run 0.5–1% higher than CPI. These are favored by UK pension funds and are deeply embedded in the Sterling bond market. They mature the inflation adjustment only at redemption, creating a "true-up" when you finally get your money back.
French OAT-i and Eurozone Linkers track the Harmonized Index of Consumer Prices excluding tobacco (HICP ex-tobacco), a European Union measure. These are newer and less liquid than TIPS but growing as the ECB manages low-inflation regimes across member states.
Real yield: the honest price of inflation protection
When a traditional 10-year bond offers 4% and an inflation-linked alternative offers 1%, the market is pricing a real yield of around 1% annually. That 1% is your expected return above inflation. If inflation comes in higher than the market expected, you've won—the higher inflation-adjusted coupon payments exceed the market's original expectation. If inflation stays low, you've settled for 1% real, which might underperform a nominal bond.
Pension funds and endowments with long-term liabilities explicitly tied to inflation (paying pensioners an inflation-linked pension, for instance) buy these bonds as natural hedges. The real yield doesn't matter as much as matching the inflation exposure of their liabilities. Retail investors with finite retirement horizons often accept lower real yields in exchange for the certainty that their bond allocation won't erode away in a high-inflation decade.
When inflation-linked bonds shine and struggle
These bonds are indispensable if you believe inflation will exceed consensus expectations, or if you simply cannot tolerate the risk of purchasing-power erosion. In the 2010s, when inflation stayed below 2% in most developed economies and central banks promised to raise it to 2%, inflation-linked bonds underperformed nominal bonds because actual inflation proved lower than the market had priced in. By 2021–2022, when inflation spiked to 8% in the US and 11% in the UK, inflation-linked bondholders benefited from principal adjustments that far exceeded what nominal bond yields could offer.
They also struggle when you face a liquidity need. The secondary market for inflation-linked bonds is narrower than for nominal Treasuries or gilts. A large redemption could move prices. And if you are forced to sell an inflation-linked bond before maturity during a period of falling inflation expectations, the real yield investors demand at that moment might be higher than when you bought, causing your price to drop.
The connection to total bond allocation
Whether you allocate to inflation-linked bonds depends on how much of your portfolio you dedicate to nominal bonds and which inflation regime you expect. A balanced investor with 30% in bonds might allocate half to nominal (benefiting from falling rates) and half to inflation-linked (protecting real wealth). In high-inflation environments, increasing the inflation-linked proportion is prudent. In low-inflation environments, the low real yield might not justify the opportunity cost versus higher-yielding corporate or international bonds.
Next
Real yield and nominal yield are not abstract concepts; they define whether a bond pays you a return that beats inflation or merely returns nominal cash that buys less tomorrow. Understanding the gap between them is the first step to deciding how much of your bond allocation belongs in inflation-linked securities versus traditional fixed-coupon bonds.