what is a series i bond 
series i bonds also known as i bonds are a type of savings bond issued by the u s treasury that offer investors a unique combination of safety and protection against inflation these bonds are considered among the most low risk investments available as they are backed by the full faith and credit of the united states government unlike traditional savings bonds i bonds earn interest through a combination of a fixed rate which remains constant throughout the life of the bond and a variable inflation rate that is adjusted twice a year based on changes in the consumer price index cpi most series i bonds are issued electronically but it is possible to purchase paper certificates with a minimum of 50 using your income tax refund according to treasury direct 1understanding series i bondsseries i bonds are non marketable bonds that are part of the u s treasury savings bond program designed to offer low risk investments their non marketable feature means they cannot be bought or sold in the secondary markets the two types of interest that a series i bond earns are an interest rate that is fixed for the life of the bond and an inflation rate that is adjusted each may and november based on changes in the non seasonally adjusted consumer price index for all urban consumers cpi u 2 i bonds are issued at a fixed interest rate for up to 30 years plus a variable inflation rate that is adjusted each may and november this gives the bondholder some protection from the effects of inflation 3the fixed rate component of the series i bond is determined by the secretary of the treasury and is announced every six months on the first business day in may and the first business day in november that fixed rate is then applied to all series i bonds issued during the next six months is compounded semiannually and does not change throughout the life of the bond 2in addition to the fixed interest rate the variable rate is announced twice a year in may and november and is determined by changes to the consumer price index cpi which is used to gauge inflation in the u s economy the change in the inflation rate is applied to the bond every six months from the bond s issue date 2in effect the interest paid on series i bonds is variable and changes over time making it difficult to forecast the value of the bonds years from today 