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. It can weaken over time due to inflation. That's because rising prices effectively decrease the number of goods or services that one unit of money can buy. Purchasing power is also known as a currency's buying power.

In investment terms, purchasing or buying power is the dollar amount of credit available to a customer based on the existing marginable securities in the customer's brokerage account.