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5 Jan 2026

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4 pages

Understanding Cost Curves in Economics

Tanvir Ahmed

@txnvir_ahmed

Cost curves are an essential concept in economics that show... Show more

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Cost Curves

Cost curves are graphical representations that show how various costs change with different levels of production. These curves are crucial tools for businesses to determine the most efficient level of output and to make strategic decisions about production.

They display the relationship between output quantity and different types of costs: fixed, variable, average, and marginal costs. By analyzing these curves, businesses can identify their most efficient production point.

Understanding cost curves helps explain why some businesses expand while others keep production limited, and how firms respond to changes in market conditions.

Fixed & Variable Costs

Fixed costs remain constant regardless of production quantity. Total Fixed Cost (TFC) is represented by a horizontal line on a graph because it doesn't change with output.

Average Fixed Cost (AFC) is calculated by dividing TFC by quantity $AFC = TFC/Q$ . AFC decreases as output increases because the same fixed cost is spread across more units.

Average Variable Cost (AVC) is found by dividing Total Variable Cost by quantity $AVC = TVC/Q$ . Initially, AVC decreases as output increases due to increasing marginal product, but then rises after reaching the Minimum Efficient Scale (MES) point due to the Law of Diminishing Marginal Returns.

Remember: The Law of Diminishing Marginal Returns states that when you add more of one production factor (like workers) to fixed factors (like equipment), productivity initially increases but eventually decreases.

Marginal Cost and Average Cost

Marginal Cost (MC) represents the cost of producing one additional unit. It typically forms a U-shape, first decreasing then increasing due to the Law of Diminishing Marginal Returns.

MC intersects Average Cost (AC) at AC's lowest point. This intersection explains a key economic principle: when MC is below AC, each additional unit lowers average costs; when MC exceeds AC, each additional unit increases average costs.

When MC equals AC, productive efficiency is achieved - this is the optimal production point. The same relationship applies to MC and Average Variable Cost (AVC).

Key insight: All cost curves together create a distinctive pattern - AFC continually falls as output increases, while AVC, AC, and MC all form U-shapes, initially falling and then rising as output increases.

Law of Diminishing Marginal Returns

The Law of Diminishing Marginal Returns is a short-run phenomenon that occurs when at least one factor of production remains fixed while others vary. In contrast, the long-run is when all factors can be varied.

This law explains what happens when you increase a variable factor (like labour) while keeping other factors fixed (like equipment or space). The extra output gained from each additional unit is called marginal product.

Initially, adding more of a factor (like workers) increases marginal product through benefits like specialisation. However, after the point of diminishing returns, marginal product begins to fall because fixed factors become limiting constraints.

Real-world example: Imagine a factory with 5 sewing machines (fixed). Adding a 6th worker when you already have 5 workers won't increase output proportionally because workers will have to share the machines, reducing efficiency.

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Economics

•

5 Jan 2026

•

4 pages

Understanding Cost Curves in Economics

Tanvir Ahmed

@txnvir_ahmed

Cost curves are an essential concept in economics that show how different costs change as production increases. Understanding these curves helps you grasp how businesses make production decisions and determine optimal output levels.

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Cost Curves

Understanding cost curves helps explain why some businesses expand while others keep production limited, and how firms respond to changes in market conditions.

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Fixed & Variable Costs

Fixed costs remain constant regardless of production quantity. Total Fixed Cost (TFC) is represented by a horizontal line on a graph because it doesn't change with output.

Average Fixed Cost (AFC) is calculated by dividing TFC by quantity $AFC = TFC/Q$ . AFC decreases as output increases because the same fixed cost is spread across more units.

Remember: The Law of Diminishing Marginal Returns states that when you add more of one production factor (like workers) to fixed factors (like equipment), productivity initially increases but eventually decreases.

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Marginal Cost and Average Cost

Marginal Cost (MC) represents the cost of producing one additional unit. It typically forms a U-shape, first decreasing then increasing due to the Law of Diminishing Marginal Returns.

When MC equals AC, productive efficiency is achieved - this is the optimal production point. The same relationship applies to MC and Average Variable Cost (AVC).

Key insight: All cost curves together create a distinctive pattern - AFC continually falls as output increases, while AVC, AC, and MC all form U-shapes, initially falling and then rising as output increases.

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Law of Diminishing Marginal Returns

Real-world example: Imagine a factory with 5 sewing machines (fixed). Adding a 6th worker when you already have 5 workers won't increase output proportionally because workers will have to share the machines, reducing efficiency.