I Bonds vs TIPS: Which Inflation-Protected Treasury Fits Your Plan

Por Beatriz
I Bonds vs TIPS: Which Inflation-Protected Treasury Fits Your Plan

“I’ve got $30,000 sitting in checking and I’m losing to inflation every month. Where do I put it?” That’s what a client said to me three years ago, and the answer then is the same answer now: inflation-protected Treasuries are the most undervalued tool in a long-term plan, and most people don’t know the difference between the two main flavors. Series I Bonds and TIPS sound like cousins. They behave like distant relatives at a holiday dinner — both polite, completely different agendas.

I’m gonna be straight with you: if you’re holding cash you won’t touch for at least a year, and you’re not using these instruments, you’re leaving real return on the table. The May 2026 I Bond composite rate sits at 4.26%, and 10-year TIPS real yields are at 15-year highs around 2.17% above inflation. Those numbers are not normal. They reward the reader who learns the mechanics this week, not next year.

The audit checklist: what to know before you buy either one

Before you sign anything, do the quick math: every inflation-protected Treasury question comes down to six variables. I run through these in order whenever a client asks me which one fits. Get the order wrong and you buy the wrong instrument for the right reason.

Here’s the audit, ranked by impact on your decision:

1. Time horizon. Money you need in under 12 months: neither. I Bonds have a hard 1-year lockup.
2. Account type. Have room in an IRA or 401(k)? TIPS belong there because of phantom income tax. I Bonds live on TreasuryDirect only.
3. Amount. Under $10,000 per person per year: I Bonds work fine. Above that ceiling: TIPS are the only practical vehicle.
4. Liquidity need. Want to sell on a secondary market at any time? TIPS. I Bonds redeem only through Treasury, with penalties before year 5.
5. Floor protection. Worried about deflation eating your principal? I Bonds have a 0% floor. TIPS real yields can go negative.
6. Tax timing. Want to defer federal tax until redemption? I Bonds let you. TIPS tax you annually on inflation adjustments you haven’t received in cash.

Run that checklist top to bottom and the answer falls out. Skip steps and you’ll buy the instrument that fits someone else’s situation.

Series I Bonds: the small-dollar workhorse

The I Bond composite rate has two engines. A fixed rate set when you buy (currently 0.90%, locked for the full 30-year life of that specific bond), and a variable inflation rate that resets every May 1 and November 1 based on CPI-U. The Treasury combines them with this formula: fixed + (2 × semiannual inflation) + (fixed × semiannual inflation). For May 2026 through October 2026, that math produces 4.26%.

The 0.90% fixed rate is the part that matters for a long-term plan. That’s your guaranteed real return above whatever inflation does for the next three decades on this specific purchase. When inflation drops, your variable piece drops with it, but the fixed piece keeps producing. I’ve analyzed thousands of bank statements. Clear pattern: clients who bought I Bonds in 2022 when the fixed rate was 0.00% are kicking themselves now that the fixed rate sits near a full percentage point higher.

The catches are real and worth knowing. You cannot touch the money for 12 months, period. Between months 13 and 60, redemption costs you the last 3 months of interest. After 5 years, no penalty. The annual purchase cap is $10,000 per Social Security Number through TreasuryDirect, and as of January 2025 the paper-bond-via-tax-refund option was eliminated. A married couple can stack to $20,000 per year. That’s the ceiling. It’s why I Bonds are a small-dollar tool, not a portfolio cornerstone.

TIPS: the big-dollar inflation hedge

TIPS work on a completely different mechanic. You buy a bond with a fixed coupon rate, and the principal adjusts up (or down) with CPI-U every six months. The coupon pays on the adjusted principal, so your interest payments rise with inflation even though the rate itself never changes. Maturities come in 5, 10, and 30 years. At the May 21, 2026 reopening auction, the 10-year TIPS produced a 2.169% real yield against a 4.60% nominal 10-year Treasury, implying a breakeven inflation rate of 2.43%.

That 2.17% real yield is doing heavy lifting in a long-term plan. It means you’re locking in inflation plus roughly two percentage points for a decade, contractually. Longer-dated TIPS real yields are at 15-year highs as of mid-2026, which is why bond nerds are quietly building 30-year TIPS ladders right now. Accrued principal on existing TIPS can often be purchased at a discount on the secondary market, which sweetens the deal further.

Here’s the part nobody wants to tell you: TIPS generate phantom income. The IRS taxes those annual inflation adjustments to principal as federal income in the year they happen, even though you don’t receive that cash until maturity. Hold TIPS in a taxable account and you’ll pay tax on money you haven’t seen. This is why TIPS belong inside an IRA or 401(k) for most people. Inside the tax shelter, phantom income disappears as a problem and TIPS become exactly what they advertise: a clean, liquid, inflation-linked real-yield instrument with no practical purchase cap.

Which one fits which goal

I split these into three buckets when I’m walking through a financial plan. Emergency fund extension, retirement inflation hedge, and education or large-purchase savings on a 5-to-10-year horizon. Each bucket has a clear winner.

Emergency fund extension past your 3-to-6-month cash cushion: I Bonds win. The 0% floor means your principal can’t be eroded by deflation, the federal tax deferral compounds quietly, and $10,000 per year per spouse builds a meaningful second-tier reserve over 3 to 5 years. Retirement inflation hedge: TIPS inside the IRA or 401(k) win, because you can deploy real money at scale, the phantom income tax issue disappears inside the wrapper, and you can build a ladder across 5-, 10-, and 30-year maturities matched to retirement income needs.

Mid-horizon goals like a college fund or a home down payment 7 to 10 years out: this is where it gets interesting. I generally prefer a blend. I Bonds for the federal tax deferral and 0% floor on the first $10,000 per year, TIPS inside a Roth IRA (if available and the goal is retirement-adjacent) for amounts above the cap. The blend protects against both inflation overshoot and deflation undershoot, which is the honest answer for goals 5+ years out where you can’t predict which regime you’ll live through.

Your next move

The unintuitive insight is this: I Bonds and TIPS are not competitors. They’re shaped to solve different problems, and the people who get the most out of inflation-protected Treasuries own both, sized correctly to the right account. Treating them as either/or is the most common mistake I see.

Three profiles, three plays:
• Under $20,000 to deploy, taxable accounts only: max out I Bonds first ($10,000 per spouse via TreasuryDirect). The 0.90% fixed rate is the best lock-in since 2008. Skip TIPS until you have IRA space.
• Funded IRA or 401(k) with room to spare: build a TIPS ladder inside the tax-advantaged account. Start with a 5-year and 10-year position to test the mechanics, then extend to 30-year as real yields permit.
• Both buckets open, $50,000+ to allocate: stack I Bonds annually for the federal tax deferral and floor protection, run a TIPS ladder inside the IRA for the large-dollar inflation hedge. This is the textbook approach and the one I use myself.

The complications are predictable. First, TreasuryDirect’s website is famously clunky and account recovery takes weeks if you lose access, so save your account number and password in two places before you fund. Second, TIPS purchased through a brokerage settle differently than I Bonds and the inflation-adjusted principal on a secondary-market purchase can confuse new buyers about cost basis at tax time. Third, if rates spike further, the I Bond fixed rate could climb again in November 2026, which tempts people to wait — except inflation is also running hot, so waiting costs you the variable piece in the meantime.

My grandmother used to say money you can’t see is money you actually save. I think she’d have liked TreasuryDirect for exactly that reason: it’s deliberately inconvenient, which is the whole point.

This week, open a TreasuryDirect account at the official TreasuryDirect portal (allow 30 minutes, have your SSN and bank routing number ready), link your checking, and schedule a $1,000 test I Bond purchase before the next rate reset on November 1. If you also want TIPS exposure, log into your brokerage and look at the secondary-market 10-year TIPS quotes, or read the maturity calendar at the U.S. Treasury homepage. Think of it like installing a smoke detector. Boring on the install day, priceless the year the kitchen catches fire.