Abstract: A system and method for calculating a number of units of a security or other investment instrument to be traded periodically in a fluctuating market in a manner that optimizes the per-unit dollar value of the corresponding transaction. The system and method each comprise equations for calculating the number of units to be purchased or sold during each of a plurality of transaction periods based upon (1) a target amount of money for purchasing, or to be received from the sale of, the security during each transaction period, (2) a non-zero baseline unit price and (3) a current per unit price during the corresponding transaction period. In one embodiment, each equation further includes a gain control that, when all other variables are fixed, allows an investor to adjust the number of units traded to suit his or investment goals and/or to suit market conditions.