As of 2026-08-09 | United States | USD | General education, not individualized financial, investment, tax, legal, credit, benefits, mortgage, or retirement advice.
I bonds and TIPS both respond to inflation, but they are not interchangeable. I bonds are nonmarketable savings bonds with redemption restrictions and a composite rate that resets; TIPS are marketable securities with inflation-adjusted principal, fixed coupon, auction pricing, and market value that can fall before maturity.
The decision in one minute
Use I bonds for eligible money that can clear the one-year lock and where deferral, redemption rules, and purchase limits fit. Use TIPS when the maturity, marketability, real yield, interim interest, and current federal tax treatment fit the liability. In May 2026, new I bonds carried a 4.26% composite rate for their first six months, including a 0.90% fixed rate; that is not a guaranteed one-year return.
- Match the security’s redemption or maturity date to the spending date.
- Compare the I-bond fixed and inflation components with the TIPS real yield and purchase price.
- Model federal tax timing, state-tax exemption, account location, and early-sale consequences.
- Do not use either security as immediate emergency cash without separate liquidity.
The practical comparison is not a slogan about which option is always better. It is a controlled test: use the same amount, dates, jurisdiction, household constraints, and risk window on both sides. Replace every illustrative input below with the current written terms that apply to you before acting.
What the official sources establish
Treasury announced a 4.26% composite rate for I bonds issued May through October 2026, including a 0.90% fixed rate; the composite applies for the first six months after issue.
I bonds cannot be redeemed during the first 12 months. A redemption before five years generally forfeits the latest three months of interest.
TIPS are marketable Treasury securities issued in 5-, 10-, and 30-year terms. Principal adjusts with inflation or deflation, coupon interest is paid every six months, and maturity pays at least original principal.
A TIPS sold before maturity can realize a market gain or loss. Federal tax can be due on coupon interest and inflation adjustments before the adjusted principal is paid at maturity; Treasury interest is exempt from state and local income tax.
These are rule and program boundaries, not a quote or forecast. Government pages can change, issuer or plan documents can be narrower, and future returns, inflation, income, tax law, eligibility, and household needs are unknown. The checked date is part of the evidence.
A reproducible comparison
This model is deliberately simple enough to audit. It is an illustration, not a prediction. Its purpose is to expose the inputs that control the decision and make it obvious where a personal document or live quote must replace an assumption.
Inputs and assumptions
- USD
- United States Treasury rules
- 2026-08-09 as-of date
- $10,000 purchase
- I-bond 4.26% annualized composite held flat only for illustration
- semiannual compounding approximation
- hypothetical TIPS 1.75% real coupon and 2.50% one-year inflation
- TIPS held rather than sold in the one-year illustration
- federal and state tax, auction price, accrued interest, and reinvestment omitted
flat-rate-i-bond-illustration
Formula: 10000 * (1 + 0.0426/2)^2 = 10430.54
Inputs: {"principal":10000,"annualizedCompositeRate":0.0426,"periods":2}
Outputs: {"illustrativeOneYearValue":10430.54,"illustrativeInterest":430.54}
Units: USD and semiannual periods. Rounding: nearest cent.
tips-inflation-adjusted-principal
Formula: 10000 * (1 + 0.025) = 10250
Inputs: {"principal":10000,"inflation":0.025}
Outputs: {"adjustedPrincipal":10250}
Units: USD. Rounding: nearest dollar.
tips-coupon-approximation
Formula: ((10000 + 10250) / 2) * 0.0175 = 177.19
Inputs: {"averageAdjustedPrincipal":10125,"couponRate":0.0175}
Outputs: {"approximateCouponInterest":177.19}
Units: USD. Rounding: nearest cent.
The I-bond calculation holds a six-month composite rate flat for a full year solely to show the arithmetic; the second six-month rate will be reset. The TIPS calculation separates principal inflation adjustment from coupon income and omits price, tax, and sale effects. It is not a yield comparison without a live TIPS quote and maturity.
Case for Series I savings bonds
I bonds avoid secondary-market price fluctuation because they are redeemed under Treasury savings-bond rules rather than sold. Federal tax deferral may be useful, and the fixed-rate component remains with the bond while the inflation component resets.
The one-year lock is absolute for ordinary holders, the under-five-year penalty reduces early value, annual purchase limits and registration rules apply, and the next inflation component is unknown. A quoted composite rate is not a full-horizon yield.
Case for Treasury Inflation-Protected Securities
TIPS can be selected by maturity and bought or sold in the market. Holding to maturity aligns the inflation-adjusted principal with a dated liability more directly than assuming a savings-bond redemption date.
Market price can fall when real yields rise, especially for longer duration. Taxable-account owners may owe federal tax on inflation adjustments before receiving principal, and auction price or brokerage spread affects the realized return.
What can flip the answer
- The spending date and whether the one-year I-bond lock can be tolerated.
- The I-bond fixed rate, future inflation components, purchase limits, and early-redemption penalty.
- The TIPS real yield, auction or market price, maturity, duration, accrued interest, and brokerage execution.
- Federal tax timing, state-tax exemption, and whether TIPS are held in a tax-advantaged account.
- Deflation, reinvestment needs, and the possibility of selling TIPS before maturity.
Run at least a base case, a less favorable case for the initially preferred option, and a household-stress case. If a modest change reverses the result, the responsible conclusion is that the choice is close. A split, a shorter commitment, or a documented review date can be more robust than forcing a winner.
Downside and failure cases
- Treating the current I-bond composite rate as a one-year guarantee.
- Using locked I-bond money for an emergency fund needed inside 12 months.
- Buying a long TIPS and assuming it cannot lose market value before maturity.
- Ignoring federal tax on TIPS inflation adjustments in a taxable account.
- Comparing an I-bond redemption value with a TIPS coupon rate while omitting purchase price and principal adjustment.
A lower payment, larger projected balance, or tax advantage is not enough by itself. Liquidity, sequence risk, reversibility, behavioral follow-through, fees, legal ownership, beneficiary or survivor effects, and the cost of being wrong belong in the same comparison. No return, approval, forgiveness, tax outcome, benefit, or savings amount is guaranteed.
Price the do-nothing option
Keeping funds in insured liquid cash preserves access while quotes and timing are uncertain, but may lose purchasing power. A short verification period is reasonable; an unplanned long cash holding should be compared with a dated inflation need and a current after-tax yield.
Doing nothing can be rational for a short verification window, but it should have an owner and an end date. Write down what evidence is missing, who will obtain it, and the date the decision reopens. Otherwise delay becomes an unmeasured option with hidden cost.
Verification worksheet
| Field | Your current value | Where to verify |
|---|---|---|
| I-bond issue date and fixed rate | ______ | TreasuryDirect account and rate table |
| next possible redemption date | ______ | TreasuryDirect savings-bond rules |
| TIPS CUSIP, maturity, and real yield | ______ | auction result or broker confirmation |
| TIPS purchase price and accrued interest | ______ | trade confirmation |
| federal and state tax treatment | ______ | current IRS guidance and tax return |
Keep the dated documents used for the comparison. Record whether a number is guaranteed, fixed, variable, estimated, projected, taxable, deductible, refundable, vested, revocable, liquid, or subject to a deadline. If two offers or calculators define a field differently, normalize them before comparing.
A bounded action sequence
- Name the inflation-linked liability and spending date.
- Keep separate cash for needs inside the I-bond lock period.
- Record the I-bond fixed rate and do not extrapolate the first composite rate.
- For TIPS, compare live real yields and maturities and decide whether holding to maturity is feasible.
- Model taxable-account cash taxes and a forced-sale scenario.
- Use TreasuryDirect and current tax guidance immediately before purchase or redemption.
Stop before signing, transferring, redeeming, converting, enrolling, changing withholding, or making an irreversible election if a required document is missing or the live terms differ materially from the example. Ask the relevant administrator or agency for written clarification. For a material tax, legal, benefits, credit, or investment consequence, use a qualified professional who can review the full facts.
Conflicts, compensation, and scope
MoneyMaxx did not receive affiliate, lender, bank, broker, issuer, plan, adviser, employer, servicer, lead-generation, referral, or sponsor compensation for this comparison. No named commercial product is ranked or endorsed. Official sources support general rules; the numerical case is labeled and reproducible.
This guide cannot see your full cash flow, contracts, tax return, filing status, basis, state law, credit file, health costs, estate plan, employment terms, plan document, risk capacity, or family obligations. Those omissions are decision inputs, not fine print.
Final stress test before acting
- Change the second six-month I-bond inflation component materially up and down.
- Redeem the I bond shortly after the one-year lock and apply the three-month penalty.
- Raise real yields and model a TIPS sale before maturity at a loss.
- Include federal tax on TIPS coupon and inflation adjustment.
- Move the spending date earlier than planned and test available liquidity.
The better instrument is the one whose lock, maturity, tax timing, and price behavior match the liability. Compare live terms on the same date; do not compare only the words inflation protected.
Primary sources checked
- Treasury May 2026 savings-bond rate release
- TreasuryDirect I-bond interest rates
- TreasuryDirect I bonds
- TreasuryDirect TIPS
- TreasuryDirect tax information for marketable securities
Source check date: 2026-08-09. Recheck the live pages and your own written documents on the day you act.
