Certificate of deposit (CD) interest rates are generally fixed. This means that when you purchase a CD, the interest rate you earn on your investment will remain the same for the entire term of the CD. The interest rate is determined when you purchase the CD and is locked in for the term of the CD, which can range from a few months to several years. This is in contrast to other types of savings accounts or money market accounts, which may have variable interest rates that can change at any time.