How Inflation-Linked Treasuries Adjust

The United States Treasury issues bonds whose principal moves with a consumer price measure. The mechanism is arithmetic rather than discretionary, and it changes how the security behaves.

The adjustment mechanism

The principal amount of an inflation-linked Treasury is restated according to a published price index, with a lag between the index reading and the date it applies.

The coupon rate is fixed, but it is applied to the adjusted principal. As principal rises, the dollar interest payment rises with it even though the stated rate has not moved.

At maturity the holder receives the adjusted principal, with a floor protecting against receiving less than the original face amount in a period of falling prices.

Real yields versus nominal yields

An ordinary Treasury quotes a nominal yield that must cover both expected inflation and a real return. An inflation-linked Treasury quotes only the real component.

The gap between the two for the same maturity is called the breakeven, and it reflects what the market is collectively pricing for inflation over that period.

Real yields can be negative, which sounds strange but simply means buyers are accepting a return below the index in exchange for the adjustment feature.

Why prices still fall

These securities are frequently misunderstood as protected from loss. They are protected against the erosion of purchasing power, not against price movement.

Their market price responds to changes in real yields the way any bond responds to yield changes, and longer maturities respond more sharply.

A period of rising real yields can therefore produce declines even while the index adjustment is running positive, which surprises holders who expected the opposite.

The lag and the index itself

The adjustment references a specific published index with a set lag, so the security does not track a household's own experience of prices.

Individual spending patterns differ from the basket the index measures, which means the protection is against a defined measure rather than against personal cost increases.

The Treasury publishes the reference figures and the adjustment factors, so the calculation is verifiable rather than estimated.

Where they fit in an allocation

Within a portfolio these securities occupy fixed income space with a different risk profile from nominal bonds, responding to real rather than nominal rate movements.

They are also available in fund form, where the same mechanics apply at the portfolio level and the distributions reflect the accrued adjustments.

How the accruals are treated depends on the account holding them and on individual circumstances, which is a matter for a qualified tax professional.