What is the difference between an SPDA, an FPDA and an equity indexed annuity?

A Single Premium Deferred Annuity (SPDA) takes one payment; a Flexible Premium Deferred Annuity (FPDA) takes many payments while it grows, such as salary reduction or bank draft; an Equity Indexed Annuity (EIA) is a fixed annuity whose interest is tied at least in part to an index such as the S&P 500, with premiums protected from index declines in most designs. All three grow tax-deferred.