How TIPS actually work

Treasury Inflation-Protected Securities, or TIPS, are marketable United States Treasury notes and bonds. Their principal is linked to the Consumer Price Index for All Urban Consumers, or CPI-U. The Treasury publishes an index ratio for each issue, and adjusted principal is original principal multiplied by that ratio.

In a simplified annual model, the identity is:

$$P_t = P_0(1+\pi)^t$$

$P_0$ is original par, $\pi$ is the inflation rate and $t$ is the number of years. With $1,000 of par, 2 percent inflation and three years, principal reaches $1,061.21 after rounding.

Actual TIPS indexation uses daily index ratios built from nonseasonally adjusted CPI-U with a publication lag. The annual model preserves the key relationship: prices move the principal base. It is not a fixed principal with a floating coupon rate.

Deflation runs the index ratio in reverse and can reduce adjusted principal between payment dates. That also reduces the coupon payment because the fixed percentage is applied to a smaller base.

A TIPS coupon rate is set when the security is auctioned and never changes. Interest is paid twice a year. Each payment equals half the annual coupon rate times the inflation-adjusted principal for that payment date.

For the examples, the annual coupon rate is 1 percent. On adjusted principal of $1,061.21, the annual coupon amount is $10.61 after rounding. The two semiannual payments divide that annual amount across the year, with each payment using the principal then in effect.

This design places inflation in two locations at once. The repayment base rises with the index, and coupon cash rises because the same fixed percentage is applied to that larger base. During deflation, both can fall before maturity.

The coupon rate is therefore not the current yield and not the real yield quoted in the market. Coupon determines cash relative to adjusted principal. Market yield determines what investors will pay for the remaining indexed principal and coupons. How bonds work explains that price and yield relationship for fixed-income cash flows.

At maturity, the Treasury pays the greater of the final inflation-adjusted principal or the security's original par. If cumulative inflation is positive, the adjusted amount is repaid. If cumulative deflation has pulled adjusted principal below original par, original par is repaid instead.

The floor applies at maturity. It does not stop adjusted principal from falling during the life of the security, so coupon payments can shrink during deflation. It also does not guarantee an investor's purchase price. A buyer who pays a market premium or pays for inflation adjustment already accrued can receive original par at maturity and still recover less than the amount invested.

The inflation index is national CPI-U, not a personal cost-of-living measure. A household concentrated in rent, health care or another category can experience a different inflation rate. Inflation and purchasing power separates the published index from an individual basket.

The maturity floor is a contractual payment rule. It is distinct from deposit insurance and from a guarantee that a secondary-market trade will be profitable.

TIPS trade in the Treasury market before maturity. Their price is the present value of inflation-adjusted payments discounted at a real yield. When market real yields rise, an existing TIPS with a lower coupon becomes less attractive and its price falls. When real yields fall, its price rises.

That means inflation protection does not remove interest-rate risk. A long-maturity TIPS can lose market value even while its principal index rises. Holding to maturity replaces the market sale price with the contractual maturity payment, provided the investor can wait, but the opportunity cost of a below-market real yield remains.

The yield difference between a nominal Treasury and a TIPS of similar maturity is called breakeven inflation. It is a market price for the inflation path at which the two securities would have similar nominal returns under simplifying assumptions. It also contains inflation risk, liquidity and market positioning, so it is not a pure forecast.

The bond price calculator shows why yields and prices move in opposite directions. TIPS add an indexed principal path to that ordinary bond pricing mechanism.

In a taxable account, both coupon interest and the year's upward principal adjustment are generally subject to federal income tax. The principal increase can be taxable even though the investor does not receive that increase in cash until sale or maturity. This is commonly called phantom income.

A downward inflation adjustment can offset taxable interest under the applicable rules, subject to limits and carry treatment. TIPS interest and inflation adjustments are generally exempt from state and local income tax, like other United States Treasury interest.

Holding TIPS in a tax-advantaged account changes the timing or treatment of that annual tax, depending on the wrapper. It does not change the index ratio, coupon calculation or market price. Tax placement and security design are separate decisions.

The real return calculator combines nominal return and inflation. How real returns work adds tax and compounding, which is the relevant bridge from an indexed security to what the investor keeps.

The examples use annual iteration to show the mechanism cleanly. The first applies 0.02 inflation for three years to $1,000 of par, producing $1,061.21 of adjusted principal and a $10.61 annual coupon amount at a 1 percent coupon rate. The second applies 0.03 for one year, producing $1,030 and a $10.30 annual coupon amount.

Actual payment dates use Treasury index ratios and semiannual coupon payments. Market value also reflects the real yield and remaining maturity, while taxable-account reporting can recognize principal adjustment before maturity. The annual examples isolate how adjusted principal feeds the coupon.

Current Treasury auction terms, index ratios and tax records supply the inputs for an actual holding. This is educational material, not financial advice.