A TIPS bought for $1,200 can still have a $1,000 floor

The U.S. Treasury building in 1857, in a salted-paper photograph attributed to Lewis Emory Walker. Library of Congress. The archival view shows the institution behind the modern repayment promise.[6]

A TIPS bought at a clean quote of 100 can cost $1,200 per $1,000 of original face value, yet its maturity floor remains $1,000. The valuation surprise sits in inflation accumulated before the trade: it enters the purchase price without raising the contractual floor.[1][2]

That gap matters when comparing an older Treasury Inflation-Protected Security with a recently issued one. Both promise inflation-linked cash flows. Their protection against a fall in the price level can nevertheless be worth different amounts. The following numbers are illustrative assumptions, not live market quotations; the exercise isolates the principal payment before considering coupons, taxes, or trading costs.

Start with the money that changes hands

Suppose an older TIPS has $1,000 of original face value and a settlement-date index ratio of 1.20. Its inflation-adjusted principal is therefore $1,200. A buyer pays for that accumulated adjustment even though the inflation happened before the buyer arrived.[2]

Treasury's pricing rules distinguish the unadjusted, or real, quote from the inflation-adjusted dollar price. Multiply the quote by the index ratio, then scale it to the original face amount. Inflation-adjusted accrued interest is added separately to obtain settlement cash.[2]

For this illustration, assume settlement on a coupon date with no accrued interest and no transaction fees:

Purchase cost = $1,000 × (100 / 100) × 1.20 = $1,200.

Nothing in that calculation resets the bond's original face value. The buyer acquires an existing contract with an existing inflation history. The higher adjusted principal is part of what changes hands; a fresh guarantee equal to the buyer's expenditure does not accompany it.

This is also why a quoted discount deserves inspection. A quote below 100 can still produce a cash purchase cost above original face value once the index ratio is applied. Reading the quote alone leaves out an entire multiplier.

Follow the principal to maturity

Treasury promises to repay the greater of original principal and inflation-adjusted principal at maturity.[1] Applied to this position:

Maturity principal = $1,000 × the greater of 1 or the maturity index ratio.

Now suppose the ratio falls from 1.20 at purchase to 1.10 at maturity. The principal repayment is $1,100. That is $100 less than the illustrative purchase cost, yet Treasury has fulfilled the contract: adjusted principal still exceeds the original $1,000 floor.

The floor contributes an additional payment only if the maturity ratio is below 1. Until then, deflation can eat into the inflation adjustment that the buyer purchased. From a starting ratio of 1.20, the relevant reference price level would have to fall by about 16.7% to reach the floor: 1 − (1 / 1.20). This is a cumulative threshold over the remaining holding period, not an annual inflation forecast.

Two accounting boundaries keep the example honest. First, the $100 shortfall compares principal paid with purchase cost; it is not the position's total return. Coupons received during ownership belong in that calculation. Second, the floor applies at maturity. It is not a standing offer to buy the security from its owner for face value.[1]

Coupons have their own exposure. Treasury calculates each semiannual payment from the applicable inflation-adjusted principal and half the fixed annual coupon rate. A lower index ratio can therefore shrink the cash interest payment even while the coupon rate stays unchanged.[3]

The older bond carries a more distant floor

The valuation consequence is subtler than “older TIPS are worse.” A recently issued bond with little accumulated inflation starts closer to the point where its maturity floor adds value. A seasoned bond can carry a substantial inflation cushion above original face value. That cushion must be exhausted before the floor provides extra principal at redemption.

In an October 2010 Economic Letter, San Francisco Fed economist Jens Christensen examined this distinction through the financial crisis. His analysis connected the divergence between seasoned and recently issued TIPS yields to the value of their embedded deflation protection. The important historical lesson is that two inflation-linked securities with similar remaining maturities can have meaningfully different floor values.[4]

My valuation inference is that a higher quoted yield on an older TIPS needs decomposition. Some of the apparent advantage may compensate for a floor that is less likely to matter. It cannot automatically be treated as free extra return. Coupon differences, remaining maturity, and execution prices also need to be controlled before attributing a yield gap to this option.

The calculation above locates the floor; it does not price the option. Estimating its present value requires assumptions about the distribution of future inflation and discount rates. A distant floor is less useful in modest deflation, but its value need not be zero.

The strongest counterweight is purchasing power

There is a good reason to accept the older bond's exposure: falling nominal principal can be consistent with the purpose of an inflation-linked investment.

In our example, adjusted principal falls in the same proportion as the reference price level. On that simplified basis, the $1,100 redemption buys what $1,200 bought at entry, before coupon income. The nominal shortfall alone therefore does not establish a failure of purchasing-power protection. It becomes consequential when the investor's goal is a fixed dollar payment, or when actual spending costs diverge from the CPI measure used by the bond.[1][5]

This counterweight changes the comparison. Someone matching a CPI-linked spending need may reasonably prefer better real cash-flow terms to a nearer nominal floor. Someone funding a fixed dollar liability has a different problem. The same security can serve one objective better than the other.

There is also a clear condition that would invalidate the above-cost exposure described here: an all-in purchase cost at or below original face value, followed by holding the bond to maturity. Under Treasury's stated repayment terms, principal redemption then covers that nominal outlay even if deflation activates the floor. That condition does not guarantee purchasing power or an attractive opportunity cost; it removes this particular principal shortfall.[1]

Three moments that resolve the valuation

At trade settlement: reconcile original face amount, clean quote, the settlement-date index ratio, accrued interest, and fees. This establishes the actual distance between the cash outlay and the maturity floor.[2]
At the next monthly CPI release: examine the non-seasonally adjusted CPI-U price level used by TIPS, then follow its incorporation into Treasury's published daily ratios. The indexing rules use lagged reference CPI and interpolation, so the headline release and a bond's daily adjustment operate on different dates.[1][2][5]
At the next coupon payment and final maturity: use the security's CUSIP and payment-date ratio to check interest, then compare terminal adjusted principal with original face value for redemption. These events reveal whether the investor is receiving the intended cash flows—and whether the floor ever contributes anything.[1][3][5]

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