A Budget Line represents the limit of a consumer’s purchasing power.

It shows the different combinations of two goods that can be purchased when:

• Income is fixed
• Prices of the two goods are known

A simplified budget equation is:

Income = (Price of Good A × Quantity of Good A) + (Price of Good B × Quantity of Good B)

For example, suppose a consumer has ₹1,000 to spend on books and meals.

If:

• One book costs ₹200
• One meal costs ₹100

Then the consumer could afford combinations such as:

• 5 books and 0 meals
• 4 books and 2 meals
• 3 books and 4 meals
• 2 books and 6 meals
• 1 book and 8 meals
• 0 books and 10 meals

Each of these combinations uses the full ₹1,000 budget.

Points:

• On the Budget Line use the full available income
• Inside the Budget Line are affordable but do not use all income
• Outside the Budget Line are unaffordable at the current income and prices

The Budget Line can shift when:

• Consumer income changes
• The price of one good changes
• The prices of both goods change

For example, if income rises while prices stay unchanged, the Budget Line shifts outward because the consumer can afford more.

Budget Lines are widely used in consumer theory to study how people make choices under limited income and competing spending options.

Choosing Between Dining Out and Movies

Suppose Rohan has ₹2,000 available for entertainment each month.

A restaurant meal costs ₹500, while a movie ticket costs ₹250.

He could spend the full budget in several ways, such as:

• 4 meals and 0 movies
• 3 meals and 2 movies
• 2 meals and 4 movies
• 1 meal and 6 movies
• 0 meals and 8 movies

All of these combinations lie on Rohan’s Budget Line.

If his monthly entertainment budget increases to ₹2,500 while prices remain unchanged, he can afford more combinations of meals and movies.

The Budget Line therefore shifts outward.

This shows how a Budget Line represents the trade-off created by limited income and the prices of different goods.

1870s – Budget Line Concept Originates with Marginalist Economists
When it happened: During development of marginal utility theory
How it happened: Helped visualize consumer choice with limited resources.

1930s – Hicks and Allen Integrate Budget Line with Indifference Curves
When it happened: 1934
How it happened: Created the modern graphical framework for consumer equilibrium.

Modern Usage – Budget Constraint Modeling in Welfare Programs
When it happened: 2000s onward
How it happened: Used to design subsidies, tax credits, and income support limits.