Series I savings bonds (“I bonds”) are U.S. Treasury securities sold to individuals through TreasuryDirect. Their composite rate combines a fixed rate set at purchase with an inflation rate that resets twice a year. They are popular as a partial cash reserve—not a full substitute for a liquid emergency fund in a high-yield savings account. Fixed-rate cousin with a long-horizon guarantee path: Series EE bonds basics.
This guide covers purchase limits, the one-year lockup, early-redemption penalty, and when T-bills or a HYSA fit better.
What an I bond is (and is not)
| Feature | Typical rule (confirm on TreasuryDirect / Treasury) |
|---|---|
| Issuer | U.S. Treasury |
| Where to buy (electronic) | TreasuryDirect.gov |
| Annual purchase limit (electronic, per SSN) | Generally $10,000/calendar year (paper via tax refund has a separate smaller cap when offered) |
| Minimum hold | 12 months before you can redeem |
| Early redemption | If you redeem before 5 years, you typically forfeit the last 3 months of interest |
| Taxation | Federal tax on interest; usually exempt from state/local income tax |
| Inflation piece | Resets every 6 months; can be low when inflation cools |
I bonds are not FDIC deposit insurance. They are backed by the full faith and credit of the United States. Deposit insurance math for bank cash still lives in FDIC/NCUA insurance in practice.
I bonds vs HYSA vs T-bills vs CDs
| Tool | Liquidity | Rate behavior | Best role |
|---|---|---|---|
| HYSA (Ally, Capital One 360, Discover Bank, many CUs) | Days | Variable APY | Core emergency cash |
| I bonds | Locked 1 year; 3-month interest penalty if under 5 years | Fixed + inflation composite | Inflation-aware surplus after the core buffer |
| TIPS | Market price can move; CPI adjusts principal | Fixed coupon on inflation-adjusted principal | Inflation-aware bond slice (tax nuance in taxable accounts) |
| Treasury bills | At maturity (or secondary market) | Discount yield at auction | Dated cash needs; Treasury ladders |
| CDs vs HYSA | Penalty if broken early | Fixed for term | Known-date surplus |
If you might need the money for a job loss next month, keep that slice in a HYSA—not in a new I bond you cannot touch for a year.
Worked example: split a $12,000 buffer
Sam has $12,000 earmarked for emergencies after paying down a 22% card.
| Bucket | Amount | Vehicle | Why |
|---|---|---|---|
| Immediate / 0–3 months of expenses | $8,000 | HYSA at an FDIC bank | Can transfer in 1–2 business days |
| Inflation-aware surplus | $4,000 | Electronic I bonds via TreasuryDirect | Willing to lock 12 months; accepts 3-month interest haircut if redeemed before year 5 |
| Not used | $0 in stocks for this goal | — | Market drawdowns and emergency timing can collide |
Sam does not put the whole $12,000 into I bonds. The one-year lock would turn a layoff into a cash crunch. After year one, they can redeem without the 12-month bar (penalty rules still apply under five years) or hold for the inflation component.
How to buy without drama
- Open a TreasuryDirect account with your SSN and a linked U.S. bank account.
- Buy electronic Series I bonds up to your annual limit. Purchases are in penny increments above the minimum.
- Record the issue date and composite rate shown at purchase.
- Set a calendar reminder at month 12 if you might need liquidity.
- Interest is generally reported for federal taxes when you redeem or when the bond final-matures—keep TreasuryDirect statements with your tax files (Filing taxes for beginners for orientation only).
Gift and entity purchase rules differ; this page covers a simple individual electronic buy.
Common mistakes
- Treating I bonds as a checking substitute
- Maxing I bonds before a three-month HYSA buffer exists
- Ignoring the $10,000/SSN electronic cap and trying to “park” a home down payment entirely in I bonds in one calendar year
- Buying from a reseller who marks up what TreasuryDirect sells at face value
Checklist
- Fund a liquid HYSA emergency core first.
- Confirm current composite rate and purchase rules on TreasuryDirect.
- Buy only surplus you can leave untouched at least 12 months.
- Stay inside annual purchase limits per SSN.
- Track issue dates and potential 3-month interest penalty before year five.
- Revisit rates each May/November inflation reset if you hold a large position.
Platform setup (auctions vs savings bonds on the same login): TreasuryDirect account basics. Older HH certificates still paying semi-annual interest: Series HH bonds basics.
Federal tax timing—defer until redemption vs report interest yearly: Series I bond tax deferral basics.
Why electronic I bonds stay on TreasuryDirect while T-bills can live at a broker: TreasuryDirect vs broker basics.
Educational only. Not investment, tax, or legal advice. Rates, purchase caps, and redemption rules change; confirm on TreasuryDirect and IRS materials before you buy or redeem.