Annuities are generally structured as either fixed or variable instruments. Fixed annuities provide regular periodic payments to the annuitant and are often used in retirement planning. Variable annuities allow the owner to receive larger future payments if investments of the annuity fund do well and smaller payments if its investments do poorly. This provides for less stable cash flow than a fixed annuity but allows the annuitant to reap the benefits of strong returns from their fund's investments.