Inflation-Protected Bonds: How TIPS and I Bonds Work

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You are paying a bill that cost noticeably less a few years ago, and the thought lands that cash and ordinary bonds pay a fixed number of dollars while prices keep moving. Inflation-linked government bonds exist to address exactly that. Treasury Inflation-Indexed Securities, known as TIPS, and Series I savings bonds are two ways of holding debt whose value is tied to changes in consumer prices. They work differently, they are taxed differently and they carry limits worth understanding before you hold either one.

Key Takeaways

• TIPS adjust their principal with changes in the Consumer Price Index, and interest is paid on the adjusted amount.
• I bonds pay a rate made of a fixed portion and an inflation portion, and the rate resets every six months.
• Both are obligations of the U.S. government, and both come with distinct rules on purchase, taxes and early sale.
• TIPS prices can fall when real interest rates rise, so they are not free of market risk before maturity.
• Which suits a situation depends on the time horizon, the account and the tolerance for rules and limits.

1. How TIPS adjust for inflation

A TIPS bond has a stated interest rate that stays fixed, but the principal it applies to changes. When consumer prices rise, the principal is adjusted upward, and the fixed rate is applied to that larger amount, so the interest payment grows. When prices fall, the principal adjusts downward. At maturity, the holder receives the greater of the adjusted principal or the original principal, so there is a floor at the original amount.

This design ties the bond's payments to a price index rather than to a fixed dollar figure. It also means the bond's yield is expressed as a real yield, meaning the return above inflation. Investors comparing TIPS with ordinary Treasury bonds often look at the gap between the two yields, which reflects what the market expects for inflation over that period. If actual inflation turns out higher than that expectation, TIPS have tended to look better by comparison, and if lower, worse.

2. How I bonds set their rate

An I bond earns a composite rate that combines a fixed rate, set at purchase and unchanged for the life of the bond, with an inflation rate that is reset every six months based on changes in the Consumer Price Index. The two pieces are combined through a formula published by the Treasury. The inflation component changes the rate you earn, and interest accrues to the bond's value and is paid when you cash it in.

The structure means the rate in the headlines at any moment is not a promise about the future, because the inflation piece resets. The fixed portion is the part that stays with the bond, and it can be low or even zero for bonds issued in certain periods. Thinking about the two parts separately gives a more accurate picture than the combined figure alone.

3. The purchase rules and limits differ

I bonds are bought directly from the Treasury, with annual purchase limits per person, and cannot be sold on a market. They cannot be redeemed during the first twelve months, and redeeming before five years costs the last few months of interest. They are not tradable, so there is no price that fluctuates.

TIPS are sold at auction and are also available through brokerage accounts and funds, which makes it easy to buy or sell on a market at any time. That flexibility is useful, but it means the price you receive before maturity can be higher or lower than what you paid. For someone with a large amount to place, the purchase limits on I bonds can be a binding constraint, while TIPS do not carry the same small annual per-person limit.

4. The two are taxed differently

Interest on both is subject to federal income tax and generally exempt from state and local income tax. The timing, though, differs. With I bonds, you can usually defer federal tax on the interest until you redeem the bond or it matures, with a reporting option to recognize it each year. With TIPS held in a taxable account, the upward adjustments to principal are generally treated as taxable income in the year they occur, even though you do not receive that money until maturity or sale. This is sometimes called phantom income, and it can create a tax bill without matching cash.

That feature is one reason many investors hold TIPS inside tax-advantaged accounts, where the annual adjustment does not create a current bill. Because the details depend on your situation, a qualified tax professional is the right person to consult.

5. TIPS carry interest rate risk before maturity

A TIPS bond adjusts its principal with inflation as measured by the index, but its market price still responds to changes in real interest rates. If real yields rise, the price of an existing TIPS falls, which can produce a loss for someone who sells before maturity, even in a period of high inflation. The longer the maturity, the larger the sensitivity.

Holding to maturity removes that price risk in the sense that you receive the adjusted principal, but it ties the money up. Funds that hold TIPS have no maturity and can show losses when real yields rise. Investors who want inflation-linked exposure with less price sensitivity sometimes choose shorter maturities, accepting a different set of trade-offs.

6. Matching the tool to the purpose

The two instruments tend to suit different situations. I bonds suit smaller amounts that can be locked away, with no market price to watch. TIPS suit larger amounts, planned future spending and accounts where taxes are deferred. Neither one keeps purchasing power intact in every circumstance, because the Consumer Price Index measures an average basket and your own spending may differ from it.

Writing down the purpose and the time horizon before choosing is the most useful discipline. It tells you whether the rules and limits matter to you, and whether you can hold to the end.

An Illustrative Week

This is an illustration, not a results claim. Imagine a physician who writes down on Sunday evening which future expenses are sensitive to rising prices and when they fall due. On Wednesday, between clinics, the physician reads the Treasury's description of both instruments and notes the purchase limits, redemption rules and tax treatment on one page. By Friday the physician has a short table matching each expense to a possible tool and a list of questions for a tax professional. Nothing was purchased. The week produced a clear map of what each instrument does and does not do.

Frequently Asked Questions

What is the difference between TIPS and I bonds?

TIPS are marketable bonds whose principal adjusts with inflation, while I bonds are savings bonds with a rate that combines a fixed part and an inflation part. They differ in how you buy, sell and are taxed on them.

Can TIPS lose value?

Yes, if you sell before maturity and real interest rates have risen, the market price can be lower than what you paid. Held to maturity, the holder receives at least the original principal.

Are I bonds taxable?

Federal income tax applies to the interest, which you can generally defer until redemption, while state and local income tax generally does not apply. A tax professional can explain how it applies to you.

Can I sell an I bond whenever I want?

Not during the first twelve months, and redeeming before five years forfeits some recent interest. After that you can redeem it with the Treasury.

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