Certificates of Deposit CDs are investments that help you grow your money safely, and using them can be as simple or as complicated as you want. Related Posts. Information that you input is not stored or reviewed for any purpose other than to provide search results. However, as secure as a CD is, there are some common mistakes to avoid that could cost you thousands. Some CDs also adjust the interest rate you earn over time. CDs are time deposit accounts issued by banks in a range of maturities, from as short as 1 month to as long as 20 years.