What Are I Bonds and How Do They Work?

I bonds are a type of savings bond issued by the U.S. Treasury designed to protect your money from inflation. They earn interest based on a combination of a fixed rate (set at purchase and locked in for the life of the bond, up to 30 years) and a variable inflation rate adjusted every six months in May and November. Because the variable component tracks the Consumer Price Index for All Urban Consumers (CPI-U), I bonds are one of the few investments guaranteed to keep pace with rising prices.

You can purchase I bonds through the TreasuryDirect website in denominations from $25 to $10,000 per calendar year per Social Security number. Paper I bonds purchased with a tax refund can add another $5,000 per year. There is a $25 minimum, and you cannot buy more than $10,000 electronically in any single calendar year.

Understanding the Two Interest Components

The composite interest rate on an I bond is calculated by combining the fixed rate and the inflation rate. The fixed rate is set when you buy the bond and never changes. If you buy an I bond when the fixed rate is 0.4%, you earn 0.4% plus the inflation adjustment for the entire 30-year life of the bond.

The variable inflation rate is reset every May 1 and November 1 based on changes in the CPI-U. For example, if inflation pushes the variable rate to 3% in May, you will earn that rate for the following six months before it is recalculated. The Treasury publishes the new rates twice a year, and the composite rate cannot go below zero, which means your principal will never decline due to interest rate changes.

Interest accrues monthly and compounds semiannually. That means your May interest is added to your principal, and then November's interest is calculated on the new, higher base. Over time, this compounding effect can meaningfully increase the value of long-held bonds.

Key Rules on Redemption and Penalties

I bonds come with specific holding rules that affect when and how you can cash them out:

  • Minimum holding period: You must hold an I bond for at least 12 months before redeeming it. Cashing out before 12 months results in the loss of all interest earned and the return of only your original principal.
  • Three-month interest penalty: If you redeem an I bond between 12 and 59 months after purchase, you forfeit the most recent three months of interest. After 60 months, the penalty disappears entirely.
  • 30-year maximum: I bonds stop earning interest after 30 years from the issue date. At that point, you should redeem them or they will simply stop growing.
  • No market loss: Unlike stocks or bonds you sell on the secondary market, the redemption value of an I bond cannot fall below your purchase price.

Tax Treatment of I Bonds

Interest earned on I bonds is subject to federal income tax but is exempt from all state and local income taxes. This makes them especially attractive for residents of high-tax states like California, New York, or New Jersey. The annual interest is reported on IRS Form 1099-INT, which TreasuryDirect generates for you each year.

One of the most valuable tax features is the ability to defer interest until redemption. You can choose to report the interest annually, which is generally not advantageous, or defer it until you file the bond. Most investors choose deferral because it allows the interest to compound tax-free until withdrawal.

Two notable tax breaks apply to I bond interest used for education:

  • The education savings exclusion allows you to exclude I bond interest from federal income tax if the proceeds are used to pay qualified higher education expenses for yourself, your spouse, or a dependent.
  • To qualify, the bonds must be purchased by the owner and used for education expenses in the same year they are redeemed. Income phaseouts apply for higher earners, with the exclusion fully phased out for single filers with modified adjusted gross income (MAGI) above $111,500 and joint filers above $186,050 in recent tax years.

Who Should Consider I Bonds and How to Buy Them

I bonds work well for several types of savers:

  • Long-term emergency fund builders: If you have a portion of your emergency fund you won't need for at least a year, parking it in I bonds offers better inflation-adjusted returns than a standard savings account.
  • Gift recipients: You can buy I bonds as gifts through TreasuryDirect, making them popular for nieces, nephews, grandchildren, or college savings.
  • Conservative investors: Investors looking to diversify away from equities will find I bonds a low-risk, government-backed option with inflation protection that TIPS and savings accounts cannot match.
  • Education savers: Families saving for college may benefit from the tax-free withdrawal feature, though they should weigh it against 529 plan benefits and contribution limits.

To buy I bonds, you must first open a free TreasuryDirect account at treasurydirect.gov. You'll need a Social Security number, a U.S. address, and a bank account for funding and redemption. After funding your account, you can purchase bonds in $25 increments up to the annual limit. Paper I bonds are still available using IRS Form 8888 during tax time if you want to direct part of your refund into savings bonds.

Current Considerations and Limitations

The annual purchase cap is one of the biggest limitations for high-net-worth investors. At $10,000 per Social Security number per year, I bonds are best suited for smaller, incremental savings rather than as a core portfolio holding. Couples can each purchase $10,000, and trusts may be able to buy additional amounts, which is a strategy some families use to multiply their annual contributions.

Rates change every six months, so timing your purchase matters. If you believe inflation will fall, buying when the variable rate is high locks in that higher semi-annual adjustment for six months. If inflation rises after purchase, the new higher rate applies regardless of when you bought. This makes I bonds particularly attractive during inflationary environments, although you cannot predict future CPI movements with certainty.

Another consideration is liquidity. Because of the 12-month minimum hold and three-month interest penalty before five years, I bonds are not appropriate for money you might need quickly. They are best used for money you can commit to a specific timeframe of at least one year, and ideally five years or longer to avoid the penalty.

Finally, I bonds are not transferable between owners except through death, divorce, or as gifts to specific recipients through TreasuryDirect. You cannot sell an I bond to another investor, which means your only exit is redemption through the Treasury.

For most Americans looking for a safe, government-backed way to grow savings with built-in inflation protection, I bonds remain one of the most attractive options available, especially for taxable accounts in high state-tax jurisdictions.