The Earnings Rate of I Bonds is a combination of two separate rates: A fixed rate of return and a semiannual inflation rate. Each May 1 and November 1, the Treasury announces a fixed rate of return that applies to all I Bonds issued during the six month period beginning with the effective date of the announcement. The fixed rate of return carried by any given I Bond will never change. Also, every May 1 and November 1 the Treasury determines a semiannual inflation adjustment based on changes in the Consumer Price Index for all Urban consumers (CPI-U). The semiannual inflation rate announced in May is a measure of inflation from October through March; the rate announced in November is a measure of inflation from April through September. CPI-U is published monthly by the Department of Labor's Bureau Labor Statistics. The semiannual inflation rate is then combined with the fixed rate of an I Bond to determine the bond’s Earning Rate for the next six months.