Inflation-Linked Bonds: When the Principal Moves With Prices

This is the direct answer to the inflation risk the opening article identified: because a normal bond's payments are nominal, an unexpected rise in prices quietly reduces what those payments buy, and no amount of creditworthiness protects against it. Governments issue instruments designed to remove that particular risk — TIPS in the US (Treasury Inflation-Protected Securities), index-linked gilts in the UK, OATi and equivalents in the euro area, and similar structures elsewhere. This article explains the mechanism, introduces the real-versus-nominal distinction that governs the whole category, and covers the honest complications — because "inflation-protected" is a precise claim rather than a general reassurance, and the ways it is misread are predictable.

The mechanism: indexing the principal

The dominant design works by adjusting the principal with a published price index, and letting the coupon follow. The bond carries a fixed real coupon rate — say 1% — but that rate is applied not to the original face value but to the index-adjusted principal, which is restated as the reference index rises. So if cumulative inflation since issue is 20%, a $1,000 bond has an adjusted principal of $1,200, and the 1% coupon pays $12 rather than $10; at maturity, the holder receives the adjusted principal, not the original face value. Both the income stream and the final repayment therefore keep pace with the index, which is exactly the protection being sold. Several structural details matter. The index and its lag: the adjustment references a specific published price index with a defined lag (commonly a few months, because index data is published in arrears), so the protection tracks measured inflation approximately rather than instantaneously — and it tracks that index, which may not match the inflation any particular household experiences. Deflation floors vary: some structures guarantee that the principal repaid at maturity is at least the original face value even if the index has fallen, while others allow downward adjustment; the terms are specific to the programme and worth reading rather than assuming. An alternative design exists: instead of indexing principal, some instruments (including certain retail savings products) adjust the interest rate periodically in line with inflation while leaving principal fixed — a different mechanism producing different cash flows and a different price behaviour. And the settlement plumbing uses an index ratio applied to the quoted price, so the amount actually paid for an inflation-linked bond involves an extra multiplication that the clean-versus-dirty price machinery from earlier in this pillar does not fully cover.

Real yields, nominal yields, and the breakeven

This category forces a distinction that runs through all of finance and is usually left implicit. A nominal yield is a return stated in currency units; a real yield is a return stated in purchasing power. Conventional bonds quote nominal yields, and their real return is unknown at purchase, because future inflation is unknown. Inflation-linked bonds quote real yields directly — the 1% in the example above is a real rate, delivered on top of whatever the index does. That is the category's whole point: it converts an unknown real return into a known one, at the cost of giving up the fixed nominal amount. Note the arithmetic implication that surprises people: a real yield can be negative, and inflation-linked bonds have at times traded at negative real yields, meaning holders knowingly accepted a small guaranteed loss of purchasing power in exchange for certainty about it — which is not irrational, and is worth understanding as a feature of how these instruments price rather than as an anomaly. The comparison between the two markets produces a genuinely useful figure. The breakeven inflation rate is the difference between the nominal yield on a conventional government bond and the real yield on an inflation-linked bond of the same maturity: it is the rate of inflation at which the two would deliver the same outcome, and therefore a market-implied measure of expected inflation over that horizon. Two honest caveats belong with it, both important. The breakeven reflects expected inflation plus risk and liquidity premia — holders may pay for inflation insurance, and the linked market is typically less liquid than the conventional one, so the figure is not a pure forecast. And it is a market price rather than a prediction, which means it moves, has been wrong, and should be read as "what the market is currently pricing" rather than "what inflation will be." This portal reports it as the former; the macro pillar covers inflation itself, and nothing here constitutes a view on where it is heading.

What the protection does and does not cover

Four honest boundaries. Interest-rate risk does not disappear. Inflation-linked bonds are still bonds: their prices move inversely with real interest rates, and a rise in real yields lowers their price exactly as the pricing article described — long-dated linkers are volatile instruments, and holders who expected "inflation protection" to mean "stable price" have been repeatedly surprised, particularly in episodes where inflation rose and real yields rose together, hurting linker prices despite the indexation working exactly as designed. This is the single most important misunderstanding in the category. The index is not your inflation. Protection tracks a national aggregate price measure, and a holder whose personal spending is weighted differently — heavier on housing, healthcare, or education, say — gets partial protection at best. Tax treatment can be awkward, because in some jurisdictions the inflation adjustment to principal is taxable in the year it accrues even though the cash arrives only at maturity — a genuine timing mismatch that materially affects the after-tax outcome and varies by jurisdiction and account type. This portal notes its existence and parks the specifics to Annex A; it is a question for a qualified tax adviser. And liquidity is generally thinner than in the conventional market for the same sovereign, with wider costs and greater sensitivity in stressed conditions. None of this argues against the instrument; all of it is what "inflation-protected" precisely means and precisely does not. Whether inflation protection is worth its cost to any particular holder depends on their horizon, their liabilities, and their view of a risk this portal does not forecast — which puts it squarely with a licensed adviser.