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Consumer Price Index (CPI)

Also called: CPI, CPI-U, inflation index

Definition: The Consumer Price Index (CPI) is a Bureau of Labor Statistics measure of the average change over time in prices paid by consumers for a representative basket of goods and services.

Updated November 11, 2026 · How we check facts

The CPI is the most widely used U.S. measure of inflation. The main index, the CPI for All Urban Consumers (CPI-U), covers urban households across the United States, a population that the BLS puts at over 90 percent of the U.S. population. The BLS publishes CPI data both seasonally adjusted and not seasonally adjusted.

Treasury uses the non-seasonally adjusted CPI-U, all items including food and energy, to set the inflation part of the Series I savings bond rate every May 1 and November 1.

Formula

Inflation between two dates is the percent change in the index:

inflation % = (CPI_new − CPI_old) ÷ CPI_old × 100

Example

If the index moves from 320.0 to 326.4, inflation over that period is (326.4 − 320.0) ÷ 320.0 × 100 = 2.0%. The index values here are illustrative. A six-month change of 2.04%, the I bond inflation rate set on November 1, 2026, is doubled to an annual 4.08% in the I bond formula.

The guide how do I bonds work shows how this inflation rate becomes the bond's combined rate.

Calculate it

Free toolSavings Bond CalculatorValue of an I bond or EE bond, with penalty and tax.Open →Free toolCompound Interest CalculatorSee what your savings grow to, year by year.Open →

Guides that explain it

How Do I Bonds Work? Rates, Rules and Value Examples

Related terms

Series I Savings BondA Series I savings bond (I bond) is a U.S. Treasury savings bond whose rate combines a fixed rate kept for 30 years with an inflation rate based on CPI-U that resets every six months.Percent ChangePercent change is the difference between a new and an original value, divided by the original value and expressed as a percentage; a positive result is an increase and a negative one a decrease.401(k)A 401(k) is an employer-sponsored retirement savings plan in which employees contribute part of their pay, often with employer matching, up to annual limits set by the IRS.Annual Percentage Rate (APR)Annual percentage rate (APR) is the cost of credit expressed as a yearly rate; for many loans it combines the interest rate with certain fees charged when the loan is made.Annual Percentage Yield (APY)Annual percentage yield (APY) is the total interest a deposit account pays over a 365-day period, expressed as a percentage that includes the effect of compounding.Catch-Up ContributionA catch-up contribution is an extra amount that people age 50 or older may add to a 401(k) or similar retirement plan above the normal annual limit, if the plan permits it.Compound InterestCompound interest is interest calculated on both the original principal and the interest already added to it, so the balance grows faster than it would with simple interest.Debt AvalancheThe debt avalanche is a repayment method that pays the minimum on every debt and puts all extra money on the highest interest rate first, which minimizes total interest.

Sources