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Macro Note 08

Why a TIPS principal can fall on paper without erasing the par floor

TreasuryDirect says the principal of a Treasury Inflation-Protected Security can go up or down over its term, but at maturity the investor receives the higher of the adjusted principal or the original amount. That means interim deflation adjustment and final principal floor are both part of the instrument.

By Hynexly Research DeskPublished Mar 30, 2026Updated Mar 30, 20263 min read2 sources

Why this note matters

TIPS are often described as if inflation protection means the principal only rises. The official Treasury language is more precise: the principal adjusts both ways over time, while the maturity payment preserves the original principal if the adjusted value finishes lower.

Key takeaways

  • TreasuryDirect says TIPS principal can go up or down over the life of the security rather than staying fixed like a nominal Treasury's principal.
  • TreasuryDirect's TIPS/CPI page says both inflation and deflation change the principal and therefore can change the size of each semiannual interest payment.
  • TreasuryDirect says that at maturity, if adjusted principal is lower than the original amount, the investor receives the original principal amount instead.

TIPS principal is adjustable by design

TreasuryDirect says that unlike other Treasury securities, where the principal is fixed, the principal of a TIPS can go up or down over its term. That is the first rule to keep in mind before reading any inflation-protection claim too loosely.

The security protects against inflation by adjusting principal, but the adjustment mechanism itself is two-sided. If inflation pushes the reference index higher, principal rises. If deflation pulls it lower, principal can decline during the life of the bond.

Coupon cash flow follows the adjusted principal

TreasuryDirect's TIPS/CPI page says the principal goes up and down with inflation and deflation and that the amount of interest paid every six months can vary because the fixed coupon is applied to the adjusted principal.

That means a reader should not treat the coupon rate and the coupon cash payment as the same thing. The rate is fixed, but the cash amount changes as the inflation-adjusted principal changes.

  • Separate the fixed coupon rate from the changing coupon payment amount.
  • Expect principal and coupon cash flow to move with the index path over time.
  • Do not confuse interim deflation adjustments with the maturity repayment rule.

The maturity floor is real, but it does not cancel the path

TreasuryDirect says that when a TIPS matures, if the principal is equal to or lower than the original amount, the investor gets the original amount. That is the principal floor many investors have in mind.

But the floor applies at maturity, not as a claim that principal never declines along the way. For Hynexly readers, the precise takeaway is cleaner: TIPS can mark down principal during deflationary periods while still preserving the original principal amount at maturity if the adjusted balance ends below par.

Source evidence snapshot

Treasury Inflation-Protected Securities (TIPS)

TreasuryDirect explains that TIPS principal can rise or fall over time and states that investors receive the greater of adjusted principal or original principal at maturity.

Open source

TIPS/CPI Data

TreasuryDirect explains that TIPS principal moves with inflation and deflation and shows how interest payments are calculated from the inflation-adjusted principal.

Open source

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