Your bond fund statement says you earned 4% last year. But groceries cost 6% more, rent went up 5%, and your insurance premium jumped 9%. Did your savings grow — or shrink? If you cannot answer that question with a number, you are measuring your wealth with a ruler made of rubber. Treasury Inflation-Protected Securities, or TIPS, exist to fix exactly that problem: they promise you a return measured in purchasing power, not in dollars that buy less every year. The mechanics behind that promise — CPI indexation, real versus nominal yield, a deflation floor, and a tax treatment that surprises nearly every first-time buyer — are worth understanding before you buy a single bond.
What TIPS Are (and What They Are Not)
TIPS are marketable securities issued by the U.S. Treasury, backed by the same full faith and credit guarantee as ordinary Treasury notes and bonds. The Treasury sells them in 5-year, 10-year, and 30-year terms, in multiples of $100, both at scheduled auctions and on the secondary market through any brokerage. The 10-year TIPS auction is the benchmark the financial press quotes when it talks about "real yields."
What makes them different from every other Treasury security is that their principal is not fixed. An ordinary $10,000 Treasury note will always repay $10,000 at maturity; only its market price moves in between. A TIPS with $10,000 of original principal will repay $10,000 adjusted for every bit of inflation — or deflation — recorded over its life. The coupon rate printed on the bond never changes, but because each interest payment is calculated on the adjusted principal, the dollars you receive change every six months.
Two things TIPS are not. They are not Series I savings bonds: I Bonds have annual purchase caps, cannot be sold for the first year, and defer federal tax until you cash them in, while TIPS trade freely with no cap and tax you every year (more on that below). And they are not a guarantee against losing money — a TIPS sold before maturity can be worth less than you paid, as the section on price risk explains.
How Your Principal Tracks the CPI
Each TIPS carries an index ratio that scales its original par value up or down with the Consumer Price Index for All Urban Consumers (CPI-U), the Bureau of Labor Statistics measure that most people mean when they say "inflation." The Treasury does not use the latest CPI headline directly: it computes a daily reference CPI by interpolating between CPI readings from about two to three months earlier, then divides by the reference CPI on the bond's dated date. That lag is why your TIPS principal on any given day reflects inflation from last quarter, not last week.
The arithmetic itself is simple. Buy $10,000 of TIPS and watch CPI-U rise 3% over the year, and your principal becomes roughly $10,300. If the bond's fixed coupon rate is 2%, your semiannual interest payments are calculated on that higher base — about $103 per payment instead of $100 — so both your principal and your income grow with inflation. If CPI-U falls instead, principal and coupon payments shrink symmetrically.
Real yield versus nominal yield
This is where TIPS rewire how you read bond quotes. An ordinary Treasury yield is a nominal yield: it tells you how many dollars you will earn, with no opinion about what those dollars will buy. A TIPS yield is a real yield: it tells you how much purchasing power you will gain on top of inflation, whatever inflation turns out to be.
The gap between the two is one of the most watched numbers in finance: breakeven inflation. If a 10-year Treasury note yields 4.2% and a 10-year TIPS yields 2.0%, the market is pricing roughly 2.2% annual inflation over the next decade. Buy the TIPS and inflation runs hotter than 2.2%, and you come out ahead of the nominal bond. Inflation runs cooler, and the nominal bond wins. You do not need a forecast to use this — you need an opinion about whether your own costs will rise faster than the market's implied guess.
The Deflation Floor at Maturity
The natural fear with a bond whose principal can fall: what if sustained deflation leaves you with less than you invested? The Treasury answers with a floor. At maturity, you receive the greater of the inflation-adjusted principal or the original par value. If you bought $10,000 of TIPS at issue and net deflation pulled the adjusted principal down to $9,200, you still get $10,000 back. You can never receive less than original par at maturity.
Three caveats keep this floor honest. First, it applies at maturity only — interim coupon payments still shrink during deflationary stretches, because they are always computed on the current adjusted principal. Second, it protects original par, not what you paid: if you bought that bond on the secondary market for $10,800 after years of inflation adjustments, the floor is still $10,000, and a deep deflation could leave you with a real loss. Third, the floor does nothing for market price. If real yields rise sharply, the market value of your TIPS falls just like any other bond, and selling early locks in the loss. The inflation protection is complete only if you hold to maturity.
The Phantom-Income Tax
Here is the feature that blindsides first-time TIPS buyers. The IRS treats each year's increase in your TIPS principal as interest income in the year it happens — even though you receive none of that cash until maturity or sale. Tax professionals call this phantom income, and it is reported to you on Form 1099-OID (for the inflation adjustment) alongside the familiar Form 1099-INT (for the coupon payments). Miss the OID form at tax time and you will underreport your income.
Put numbers on it. Hold $100,000 of TIPS in a taxable brokerage account during a year when inflation runs 3.4%, and you owe federal income tax on roughly $3,400 of phantom income plus your coupon interest — funded from your own pocket, because the bond sent you no corresponding cash. In a high-inflation year across a large position, that tax bill without cash flow is a genuine liquidity event, not a footnote.
Three mitigations matter. First, TIPS interest — both the coupons and the inflation adjustments — is exempt from state and local income tax, like all Treasury interest, which softens the bite if you live in a high-tax state. Second, in a deflation year the downward principal adjustment reduces your taxable interest income for that year (though not below zero), so the tax code gives a little back when prices fall. Third, and most practically: hold TIPS inside an IRA or 401(k), where the annual phantom-income tax disappears entirely and the inflation protection compounds untouched. There is no additional tax on the principal increase when the bond finally matures — you already paid tax on it year by year.
Mistakes TIPS Buyers Make
Beyond the tax surprise, four errors show up repeatedly.
Assuming CPI-U is your inflation. TIPS hedge the official national index, not your household budget. If your spending tilts toward categories rising faster than average — housing in a hot metro, healthcare, college tuition — your personal inflation can outrun CPI-U for years, and TIPS will undercompensate you by the difference. They hedge general inflation, not your cost of living.
Ignoring price risk on long maturities. A 30-year TIPS has the duration of a 30-year bond. When real yields rose sharply in 2022, long-dated TIPS funds fell more than 25% — inflation protection did nothing for investors who needed to sell. Match the maturity to money you can truly leave alone, or accept that the protection only fully works at maturity.
Confusing TIPS with I Bonds. Both adjust for inflation, but I Bonds cap purchases (currently $10,000 per person per year in electronic form plus up to $5,000 in paper bonds with a tax refund), forbid sales in year one, dock three months of interest if sold before five years, and defer all federal tax until redemption. TIPS have no caps, trade any business day, and tax you annually. They solve different problems: I Bonds are flexible small-scale savings; TIPS are portfolio-grade instruments at any scale.
Buying at a premium without understanding the floor. As noted above, the maturity floor covers original par, not your purchase price. A TIPS bought on the secondary market well above par after a decade of inflation has genuine downside in a deflationary scenario. Check the index ratio — your broker quotes it — before you assume the floor protects your cost basis.
Tracking TIPS in Your Own Books
If you keep personal books in plain-text accounting, TIPS deserve more care than a nominal bond, because the asset balance, the income, and the tax basis all move every year without a single cash transaction. Record the inflation adjustment as interest income that increases the asset balance — that keeps your books consistent with the 1099-OID your broker will send, and it means your cost basis tracks the adjusted principal so you do not overpay tax again at maturity or sale.
A minimal pattern looks like this. Suppose you buy $10,000 of 10-year TIPS at auction, receive a $112.50 semiannual coupon on slightly inflated principal, and book a $280 inflation adjustment at year end:
2026-01-15 * "Buy 10-year TIPS at auction"
Assets:Brokerage:TIPS-2036 10,000.00 USD
Assets:Brokerage:Cash -10,000.00 USD
2026-07-15 * "TIPS semiannual coupon on adjusted principal"
Assets:Brokerage:Cash 112.50 USD
Income:Interest:TIPS-Coupon -112.50 USD
2026-12-31 * "TIPS inflation adjustment to principal (OID)"
Assets:Brokerage:TIPS-2036 280.00 USD
Income:Interest:TIPS-Inflation -280.00 USDSplitting coupon income from inflation-adjustment income in separate accounts pays off at tax time: the two lines map directly onto your 1099-INT and 1099-OID, and a balance-sheet report always shows the bond at its current adjusted principal. If you hold several TIPS issues, give each maturity its own asset account so an index ratio check against TreasuryDirect takes seconds. Dashboards like Fava render these accounts into income and net-worth charts with no extra setup, which makes the slow compounding of inflation adjustments visible year over year.
Your Next Step
TIPS answer one question precisely: what return will I earn above inflation if I hold to maturity? Everything else — the CPI lag, the secondary-market price swings, the annual tax on money you have not received — is the cost of that precision. Before buying, do three things. First, compare the breakeven inflation rate against your honest expectation for your own costs over the holding period; TIPS win only if reality exceeds the market's guess. Second, decide where the bond lives: a retirement account neutralizes the phantom-income problem completely, while a taxable account demands a cash plan for the tax bill. Third, match the maturity to money you will not need early, because the inflation guarantee is a maturity benefit and the market price in between answers to real yields. Get those three decisions right, and the rubber ruler becomes a steel one.
