Purchasing power is the value of a currency expressed in terms of the number of goods or services that one unit of money can buy. Purchasing power is important because, all else being equal, inflation decreases the number of goods or services you would be able to purchase. In investment terms, purchasing power is the dollar amount of credit available to a customer to buy additional securities against the existing marginable securities in the brokerage account. Purchasing power may also be known as a currency's buying power.