If the system of consumer preferences is described using indifference curves, the budget line shows many options that are available to him.
Since its position and the size of the region limited by this line, with budgetary opportunities, depend on the income itself and the relative prices of goods, any changes in them lead to a certain shift.
The budget line displays all sorts of combinations of two products purchased with a fixed amount of prices and cash income.
Key Terms
In addition to the budget line, there are other terms. Thus, the line of budget constraint shows the availability of consumer sets at specific prices and incomes.
Budget space is the area of choice available to the consumer.
The indifference curve displays different combinations of several economic benefits with the same utility for the consumer.
The budget set is the set of some consumer sets that are available to a particular consumer at a certain price level and fixed disposable income. This indicator requires that a certain amount of money spent on the consumption of certain goods does not exceed the finances that the consumer is able to spend.
A bit of history
Significant contribution to the theory of ordinal utility was made by such scientists as V. Pareto, F. Edgeworth, E. Slutsky and J. Hicks. These scientists proposed the measurement of subjective utility using not an absolute, but a relative scale that shows consumer preference. 
In this case, the consumer must choose between a certain set of benefits (for example, in order to simplify, two such benefits can be considered).
Budget Line Properties
The following budget line properties are known:
1. A budget line with a negative slope characterizes the sets of goods that are on it, have the same value. Also, with an increase in the value or number of purchases of one good, it can only be with a simultaneous reduction in the acquisition of another good. Like any line, the curve of the budget line, expressing the feedback of some variables, is characterized by a negative slope.
2. The location of the budget line is directly dependent on the amount of consumer income. An increase in its value at constant prices can lead to its parallel movement. A decrease in the value of cash consumer income at constant prices shifts the budget line parallel to the left. At the same time, changes in consumer income do not change the angle of its inclination, however, they make changes to the points of the budget line (the coordinates of its intersection with the axes).
3. The slope coefficient of the budget line is equal to the ratio of prices for the benefit, taken with the opposite sign. This coefficient shows the ratio of one price of goods, which is measured horizontally, to the same indicator calculated vertically.
4. Change in product prices, which can lead to changes in the direction of the line angle. Thus, changes in the price for one good can lead to changes in the angle of inclination, as well as changes in the points of intersection with the coordinate axes.
Change in the position of the budget line with changes in consumer income
Consider how the budget line will change if any changes in consumer income are traced. At the first stage, suppose that consumer income increases when there is an unchanged price relationship between the two goods.In this case, the slope of the budget line will remain unchanged. As a result, the line itself should shift to the right and become parallel to the previous position. In this case, we can talk about expanding the budgetary possibilities of the individual, increasing his real income, expressed in units of both types of goods. With a decrease in consumer income, the budget line will shift in parallel to the left.
Analysis of indifference curves
When analyzing indifference curves, it is necessary to consider the desires of the consumer. So, thanks to the study of budget lines, you can establish the capabilities of such a consumer. 
He is preferable to be on the budget line at the highest point. With limited income, he is forced to satisfy only those desires that will not go beyond his financial capabilities. At the same time, they will make the best choice only if he manages to satisfy his own needs as much as possible within the framework of budgetary opportunities. In other words, being able to maximize the overall utility of the goods consumed.
To determine the possibilities for the consumer to achieve this situation, it is necessary to combine analyzes of desires and opportunities. To do this, it is necessary to put the budget line on the card of indifference. When determining the optimal choice point on this map, it is necessary to take into account the fact that it will be located on the budget line. Only in this way will the consumer’s income be spent in full.
Budget line feature
The line of budgetary restriction cannot allow the consumer to go beyond its limits, since this directly depends on the level of its income. 
Location on the budget line is a necessary but not sufficient condition for optimal consumer choice. This is due to the fact that different points on this line characterize a different structure of satisfied needs.
Moreover, only at one point the behavior of any consumer can be optimal with maximizing the overall usefulness of the set of benefits.
