A certificate of deposit (or CD) is a savings instrument offered by a bank or credit union that has a fixed date of maturity and a fixed interest rate. Most CDs require a minimum deposit amount and may offer rates contingent on the size of the deposit. The interest you earn on your deposit depends on the interest rate, the term of the deposit and the compounding method. Deposits that compound with greater frequency will have a higher Annual Percentage Yield, or APY. Your APY is the effective annual rate of return once the effect of compounding interest is factored in. Most CDs restrict access to the funds until the CD reaches its maturity date.