TIPS and Breakeven Inflation: The Real Yield Math
How TIPS principal indexing works, how to subtract the real yield from the nominal one to get breakeven inflation, and the tax and duration traps.
A nominal Treasury bond promises you a fixed number of dollars. If inflation runs at 2% a year for a decade, those dollars buy less when they arrive, and nobody adjusts the cheque. TIPS exist to remove that specific uncertainty: the principal is rewritten every day to track a published inflation index, so the bond pays you back in dollars of roughly the same purchasing power you lent.
The useful part for an investor is not the mechanism itself but the number the mechanism creates. Because TIPS and ordinary Treasuries of the same maturity trade side by side, subtracting one yield from the other gives the inflation rate the market is pricing. That figure - the breakeven - is quoted daily and is one of the few clean readings of what bond buyers actually expect.
How a TIPS Actually Works
Three mechanics cover almost everything:
- The principal is indexed. A $1,000 TIPS issued when the consumer price index stands at some reference level has its principal multiplied by an index ratio as CPI moves. If CPI rises 10% over the bond's life, the principal becomes $1,100.
- The coupon is a fixed rate applied to the adjusted principal. A 2% coupon on that $1,100 principal pays $22 a year, not $20. Both the coupon and the principal therefore scale with inflation.
- Deflation is only partly symmetrical. If CPI falls, the principal adjusts downward and the coupon falls with it. At maturity, though, you receive the greater of the adjusted principal or the original par value - so a cumulative deflation scenario does not leave you with less than face value at the end.
What TIPS do not protect against is the price moving before maturity. A TIPS bond is still a bond: if real yields rise after you buy, its market price falls. The inflation protection is real but it applies to the cash flows, not to the resale value at an arbitrary date.
Real Yield, Nominal Yield, and the Fisher Relationship
The yield quoted on a TIPS is a real yield - a return above inflation. The yield on an ordinary Treasury is a nominal yield - a return that includes whatever inflation turns out to be.
The exact relationship is:
(1 + nominal) = (1 + real) x (1 + inflation)
The common shorthand "nominal equals real plus inflation" is an approximation that is fine at low rates and drifts at higher ones. At a 1.9% real yield and 2.4% inflation, the approximation gives 4.3% and the exact calculation gives 1.019 x 1.024 - 1 = 4.35%. Over ten years that half-percentage-point difference compounds to roughly 5% of your money, which is why the exact form is worth using in any spreadsheet you build.
Breakeven Inflation: The Number to Watch
Breakeven inflation is simply the nominal yield minus the real yield for the same maturity. If the 10-year nominal Treasury yields 4.30% and the 10-year TIPS yields 1.90%, the breakeven is 2.40%.
That 2.40% has a precise meaning: it is the average annual inflation rate at which the two bonds deliver the same total return if both are held to maturity. Above it, TIPS win. Below it, the nominal bond wins. It is a threshold, not a forecast, although it is widely read as one.
Worked Example: Same Money, Two Bonds
Assumptions, stated so you can reproduce them: a $10,000 investment, ten-year maturities, a nominal Treasury yielding 4.30%, and a TIPS with a 1.90% real yield. Both held to maturity, coupons reinvested, no taxes, no transaction costs. The TIPS delivers approximately its real yield in purchasing-power terms whatever inflation does - that is what a real yield means when held to maturity.
| Realised inflation | TIPS nominal return | Nominal bond | Difference |
|---|---|---|---|
| 1.0% a year | 2.92% | 4.30% | -1.38 pts |
| 2.0% a year | 3.94% | 4.30% | -0.36 pts |
| 2.4% a year | 4.35% | 4.30% | +0.05 pts |
| 3.0% a year | 4.96% | 4.30% | +0.66 pts |
| 4.0% a year | 5.98% | 4.30% | +1.68 pts |
| 5.0% a year | 7.00% | 4.30% | +2.70 pts |
The TIPS column is calculated as (1.019 x (1 + inflation)) - 1, which is the real yield compounded with the realised inflation rate. The nominal column never moves, because that is the entire point of a nominal bond.
The asymmetry in the table is the honest summary of the trade. TIPS give up a little in low-inflation outcomes and gain substantially in high-inflation ones. Buying them is not a bet that inflation will be high; it is a decision to stop losing sleep over which way it goes.
Why Holding to Maturity Matters So Much
An individual TIPS held to maturity locks in its real yield, because you receive the adjusted principal and the coupons regardless of what the price did in between. A TIPS fund has no maturity date. It maintains a roughly constant duration, so its share price moves with real yields and never converges back to par.
That difference is not a technicality. A fund with an average duration of seven years loses roughly 7% of its value for each one-percentage-point rise in real yields, and it does not heal through maturity the way a single bond does. If your reason for owning TIPS is a known future liability - retirement spending in 2040, say - individual bonds or a defined-maturity fund match the job. A perpetual fund does not.
The Tax Detail That Surprises People
The annual increase in a TIPS principal is taxable in the year it accrues, even though you do not receive that money until maturity. It is reported on Form 1099-OID as original issue discount, and taxed as ordinary interest income. The coupon is taxed the same way.
The practical consequence: in a taxable account, a TIPS can generate a tax bill larger than the cash it pays you, forcing you to fund the difference from elsewhere. In a tax-deferred account - an IRA or a 401(k) - that problem disappears entirely, which is why TIPS are usually discussed as a tax-advantaged holding. State and local tax treatment of Treasury interest is generally favourable, but confirm the rules where you live rather than assuming.
Reading the Breakeven Curve, Not Just One Point
A single breakeven tells you one number. The set of breakevens across maturities tells you the shape of the market's inflation expectations, and the shape is often the more informative part. Using the same arithmetic on three maturities:
| Maturity | Nominal yield | TIPS real yield | Breakeven |
|---|---|---|---|
| 5 years | 4.10% | 1.62% | 2.48% |
| 10 years | 4.30% | 1.90% | 2.40% |
| 30 years | 4.55% | 2.20% | 2.35% |
This shape - short breakevens above long ones - says the market expects inflation to run a little above its long-run level for the next few years and then settle. A curve sloping the other way says the opposite. Neither reading tells you what will happen, but the comparison is far more useful than treating the ten-year number in isolation, because it separates "inflation is high right now" from "inflation is expected to stay high".
One caution when comparing maturities: the liquidity premium is not constant across the curve. Short TIPS are more actively traded than thirty-year ones, so part of any slope you observe is a liquidity effect rather than a change in expectations.
What TIPS Do Not Do
- They do not protect against unexpected inflation in the short run. If inflation spikes and the central bank responds by raising real yields, the market price of your TIPS can fall by more than the inflation adjustment adds. The protection is a maturity-horizon promise.
- They do not protect against the inflation you actually experience. CPI measures a national basket. If your personal basket is dominated by rent and healthcare in a city where both rose faster than the index, your real return is lower than the stated one.
- They are not a growth asset. A 1.9% real yield is a real yield of 1.9%. Over thirty years that preserves purchasing power and very little else.
- They are not a substitute for cash. Duration risk means the value fluctuates; money you need next year does not belong in a ten-year bond.
How to Read the Pair of Yields Yourself
- Find the nominal Treasury yield and the TIPS real yield for the same maturity. Both are published daily by the Treasury and shown on most bond data pages.
- Subtract: nominal minus real gives the breakeven in percentage points.
- Compare that breakeven with your own expectation and, more importantly, with your own sensitivity. If a 1% inflation surprise would materially damage your plan, the breakeven being "expensive" is not the deciding factor.
- Check the duration before buying any fund version, and check whether the holding sits in a taxable or tax-deferred account.
None of this tells you which bond will outperform. It tells you the price the market is charging for inflation protection, which is the piece of information you actually need in order to decide whether the insurance is worth its premium.
For the related mechanics, see how duration turns a yield change into a price change. For the arithmetic of returns after inflation, see inflation and real return.
This article is general financial education, not investment advice or a recommendation of any security. Yields, index ratios and tax rules change; TIPS involve interest rate risk and can lose value before maturity. Consider consulting a qualified financial professional about your own situation.
By The Long View editorial team · How we check our guides
