Series I Bond

August 25, 2024 Fixed Income

A Series I bond is a nonmarketable U.S. savings bond whose composite rate combines a fixed component with an inflation component.

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A Series I bond is a nonmarketable U.S. savings bond whose interest rate combines a fixed rate with an inflation-linked rate. I bonds are bought and held through TreasuryDirect or eligible tax-refund purchases, accrue interest monthly, and are redeemed through Treasury rules rather than traded in the secondary market.

Key Takeaways

Series I bonds are retail U.S. savings bonds, not marketable Treasury bonds.
The composite rate combines a fixed rate set at purchase with an inflation rate that Treasury updates every May and November.
Interest accrues monthly and compounds semiannually; the owner receives the interest when the bond is redeemed or reaches final maturity.
Redemption rules, purchase limits, tax treatment, and current rates should be verified on TreasuryDirect before relying on any summary.

Composite Rate Formula

\text{Composite Rate} = \text{Fixed Rate} + (2 \times \text{Semiannual Inflation Rate}) + (\text{Fixed Rate} \times \text{Semiannual Inflation Rate})

The fixed rate applies for the life of the bond. The inflation component changes every six months based on changes in non-seasonally adjusted CPI-U. A bond’s composite rate can go down when inflation falls, but TreasuryDirect states that an I bond’s interest rate will not fall below zero.

How Series I Bonds Work

Feature	Series I Bond Treatment
Marketability	Nonmarketable savings bond; it is not bought and sold on an exchange.
Rate structure	Fixed rate plus inflation component.
Interest	Accrues monthly and compounds semiannually.
Redemption	Generally unavailable during the first year; early redemption before five years forfeits recent interest under Treasury rules.
Tax	Federal tax applies; state and local income tax treatment differs from many other investments.
Best source	TreasuryDirect for current rates, limits, redemption rules, and tax forms.

Series I Bonds vs. TIPS

Feature	Series I Bond	Treasury Inflation-Protected Securities
Investor access	Retail savings bond program.	Marketable Treasury security.
Inflation link	Composite rate includes inflation component.	Principal adjusts with CPI-U.
Cash flow	Interest is paid at redemption or maturity.	Interest is paid every six months.
Liquidity	Redeemed through Treasury rules.	Can be sold before maturity at market price.
Main risk focus	Redemption timing, current rate period, tax timing, and purchase limits.	Real yield, market price, tax timing, and maturity.

Practical Example

An investor buying an I bond for emergency cash would need to notice that the bond generally cannot be redeemed during the first year. An investor comparing I bonds with TIPS should compare liquidity, rate-reset mechanics, tax timing, purchase limits, and whether they need periodic cash interest or can wait until redemption.

Common Mistakes

Treating an I bond as cash despite redemption restrictions.
Assuming the current composite rate applies forever.
Confusing the fixed rate with the total composite rate.
Treating I bonds and TIPS as interchangeable inflation hedges.
Ignoring tax reporting choices and education-related tax rules that may depend on personal facts.

Public Source Checks

TreasuryDirect I bonds explains I bond rate components, interest accrual, redemption rules, and tax basics.
TreasuryDirect I bond rates publishes current and historical I bond composite rates and fixed-rate components.
TreasuryDirect cashing savings bonds explains redemption timing and early-redemption penalties for EE and I savings bonds.
TreasuryDirect comparing EE and I bonds compares current EE and I bond features.

Savings Bond: Broader U.S. savings bond category.
Series EE Bond: Fixed-rate savings bond series with different Treasury rules.
Consumer Price Index: CPI-U changes drive the I bond inflation component.
Inflation-Indexed Securities: Broader category for securities linked to inflation measures.
Tax Benefits: Some savings-bond tax outcomes depend on eligibility rules.

FAQs

Is a Series I bond a marketable security?

No. A Series I bond is a nonmarketable U.S. savings bond. It is redeemed through Treasury rules rather than sold in the secondary market.

Does the I bond rate stay the same forever?

No. The fixed rate stays with the bond, but the inflation component changes every six months under Treasury’s formula.

Can an I bond be used for immediate cash needs?

Usually not. Treasury redemption rules restrict redemption during the first year and impose an interest penalty if the bond is redeemed before five years.

Revised on Sunday, June 21, 2026

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