In economics, a budget constraint represents all the combinations of goods and services that a consumer may purchase given current prices within his or her given income. Consumer theory uses the concepts of a budget constraint and a preference map as tools to examine the parameters of consumer choices . Both concepts have a ready graphical representation in the two-good case. The consumer can only purchase as much as their income will allow, hence they are constrained by their budget. The equation of a budget constraint is ${\displaystyle P_{x}x+P_{y}y=m}$ where ${\displaystyle P_{x}}$ is the price of good X, and ${\displaystyle P_{y}}$ is the price of good Y, and m is income.