I Bond Interest Rate: How It’s Set and Updated

The interest rate on a U.S. Series I savings bond is a composite rate that combines a fixed rate, which stays with the bond, and an inflation rate that changes every six months. The U.S. Treasury announces new rates twice a year; the rate for a bond you already own does not reset on announcement day, but changes according to its issue month.

How the I bond rate is calculated

The composite rate uses two components: the fixed rate and the semiannual inflation rate. The Treasury’s formula is:

Composite rate = fixed rate + (2 × semiannual inflation rate) + (fixed rate × semiannual inflation rate)

Rates are expressed as decimals in that calculation. For example, if the fixed rate were 1.20% and the semiannual inflation rate were 1.50%, the calculation would be 0.012 + (2 × 0.015) + (0.012 × 0.015) = 0.04218, or 4.218%. The published composite rate is rounded to three decimal places as a percentage, so this example would be 4.218%.

The inflation component is based on changes in the Consumer Price Index for All Urban Consumers (CPI-U), a measure of consumer prices. It reflects inflation over a six-month period rather than predicting future inflation. If the inflation rate is negative, the composite rate can fall, but the bond’s redemption value cannot be less than the amount paid for it.

Fixed rate and inflation rate: what each means

• Fixed rate: Set when a bond is issued and remains the same for that bond for its life. It is not the same as the bond’s total composite rate.
• Semiannual inflation rate: A variable component that is updated every six months using CPI-U data. It applies to bonds according to their issue timing.
• Composite rate: The combined annualized rate used to calculate interest accrual for a particular six-month period. It may change as the bond moves through later periods.

A new bond’s fixed rate may differ from the fixed rate on bonds issued earlier. Consequently, two I bonds held during the same calendar period may earn different composite rates, even though their inflation components for a given reset period are tied to the same published inflation data.

When a bond’s rate changes

The Treasury announces new rates in May and November. Those announcements apply to newly issued bonds and also establish the next inflation-rate period for existing bonds. An individual bond’s six-month periods start with its issue month, however, so its rate usually changes on the first day of the month six months after it was issued, then every six months after that.

For example, an I bond issued in March has rate periods that begin in March and September. A new rate announced in May does not immediately change that bond’s rate in May; the applicable change arrives at the bond’s next six-month reset. This issue-month schedule is why an announcement date alone does not tell an existing bond owner exactly when their rate changes.

Interest is added to the bond’s value monthly and compounded semiannually. TreasuryDirect’s displayed value may not include the most recent three months of interest if the bond is less than five years old, because redeeming it before five years results in a penalty equal to the last three months of interest. That adjustment affects the displayed redemption value, not the rate formula itself.

How to check the rate on your I bond

To find the rate that applies to a specific bond, use its issue month and fixed rate rather than relying only on the latest headline rate. TreasuryDirect account holders can view their bond details and current value online; paper bond owners can use the Treasury’s savings-bond tools or contact TreasuryDirect for information.

1. Find the bond’s issue month and year.
2. Identify its fixed rate, if available in the bond details.
3. Use the issue month to determine when its six-month rate periods begin.
4. Check the Treasury’s published rate information for the relevant period, and distinguish the composite rate from the fixed-rate component.

A rate announcement reports annualized rates. It does not mean that the same percentage is credited as interest in a single six-month period. For a rough estimate, a 4% annualized rate corresponds to about 2% of value over six months before considering compounding and the exact rate-period timing.

Limits, redemption, and common misunderstandings

I bonds are designed to preserve purchasing power over time, but their value and access rules are not the same as a bank account balance. They cannot be redeemed during the first 12 months after purchase. If redeemed before five years, the last three months of interest are forfeited. After five years, that early-redemption penalty no longer applies. Bonds continue earning interest for up to 30 years.

• The rate is not locked for the entire life of the bond. Only the fixed-rate component remains constant; the inflation component resets.
• The announced rate is not necessarily your bond’s current rate. Existing bonds follow issue-month reset schedules.
• A high published rate does not guarantee the same return in later periods. Future inflation readings can raise or lower subsequent composite rates.
• The rate is not a guaranteed real return. The inflation adjustment tracks past CPI-U changes, and the fixed component can be zero or positive depending on the issue period.

Interest is generally subject to federal income tax, but not state or local income taxes. Federal tax may be deferred until redemption or another taxable event under applicable rules; check current Treasury and tax guidance for your circumstances. This article explains how the rate works, not individual tax treatment.

Frequently Asked Questions

What is the current interest rate on I bonds?
The current rate depends on the bond’s issue period and, for an existing bond, its six-month reset schedule. The Treasury publishes updated rates in May and November, so check its official rate announcement for the current period rather than assuming every bond earns the newly announced rate immediately.

Is the I bond rate fixed for the whole bond term?
No. The fixed-rate component stays constant for the bond, but the inflation component changes every six months. The composite rate can therefore change during the bond’s term.

How often does an I bond rate change?
It changes every six months for an individual bond. The exact reset months depend on its issue month, even though new rates are announced nationally in May and November.

Can an I bond’s rate be zero?
The composite rate cannot cause the bond’s redemption value to fall below its purchase price. If inflation is negative, the inflation component can reduce the composite rate, but the bond’s value floor protects the original principal.

Does the published annual rate mean I earn that much in six months?
No. The quoted composite rate is annualized. A six-month period earns roughly half that rate, with the exact value affected by the bond’s accrual and compounding rules.

Where to verify published rates

For the official fixed and inflation components, consult the U.S. Treasury’s Series I savings bond rate announcement and savings-bond information pages. Those sources explain which issue periods the announced rates cover. Because the rate changes over time and each bond follows its own schedule, checking the official details is more reliable than using a single rate figure without its date or issue-period context.

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