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# CA Foundation | Theory of Cost | Chanakya Commerce Classes

CA Foundation Paper 4 Business Economics Theory of Cost chapter-wise study material for May 2026 exam onwards by Chanakya Commerce Classes.

Canonical URL: https://www.chanakyaclasses.com/notes/theory-of-cost

CA Foundation · Paper 4 · Business Economics
Theory of
Cost
Unit 2 · Chapter 3 · MCQ-focused revision sheet for May 2026 exam onwards
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MCQ Priority
Concept Clarity
Quick Revision
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Study material aligned with the current Business Economics section.
All Economics Units
Practice MCQs
Theory of
Cost
Unit 2 · Chapter 3 · MCQ-focused revision sheet for May 2026 exam onwards
MCQ Priority
Concept Clarity
Quick Revision
Crux First
What to remember for MCQs
Cost =
Monetary value of resources used
.
Explicit cost vs Implicit cost
is very important.
Accounting cost
is not equal to
Economic cost
.
Fixed vs Variable cost
is the core short-run concept.
TC = TFC + TVC
AFC, AVC, ATC and MC relationships
are very frequently asked.
MC cuts ATC and AVC at their minimum point
.
Cost curves mainly follow
U-shaped logic
.
Opportunity cost
= next best alternative forgone.
Shutdown point
= minimum AVC.
1. Meaning of Cost
Basic Idea
Cost means the
value of inputs used in production
.
It includes payments made for resources such as labour, materials, land and capital.
Examples
Labour wages
Raw material
Rent
Interest
2. Types of Cost
1. Explicit Cost
Explicit costs are
paid in cash
.
They are
recorded in the books of accounts
.
Examples: wages, rent, electricity charges.
2. Implicit Cost
Implicit costs are not paid in cash but represent the
opportunity cost of own resources
.
Examples:
Rent of own building
Owner’s salary
Economic Cost = Explicit Cost + Implicit Cost
Accounting Cost = Only Explicit Cost
Very Frequently Asked:
Economic cost includes both paid-out cost and the value of self-owned resources. Accounting cost includes only paid-out expenses.
3. Opportunity Cost
Definition
Opportunity cost is the
value of the next best alternative sacrificed
.
Example
If a machine is used for Product A instead of Product B, then profit from Product B is the opportunity cost.
MCQ Trap
Opportunity cost is not historical cost.
It is not accounting cost.
It is a
future-oriented decision concept
.
4. Fixed Cost vs Variable Cost
Fixed Cost (TFC)
Fixed cost does
not change with output
.
It exists even when output is zero.
Examples: rent, salary of permanent staff.
Variable Cost (TVC)
Variable cost
changes with output
.
Examples: raw material, power.
TC = TFC + TVC
Direct MCQ:
Total cost is always equal to total fixed cost plus total variable cost.
5. Short Run Cost Concepts
1. Total Cost (TC)
TC = TFC + TVC
2. Average Fixed Cost (AFC)
AFC = TFC / Q
AFC always falls as output rises.
Reason: fixed cost gets spread over more units.
3. Average Variable Cost (AVC)
AVC = TVC / Q
AVC is generally
U-shaped
.
4. Average Total Cost (ATC)
ATC = TC / Q
ATC = AFC + AVC
5. Marginal Cost (MC)
MC = Change in TC / Change in Q
Marginal cost mainly depends on change in
variable cost
, because fixed cost does not change.
6. Cost Curve Relationship
Most Important MCQ Logic
MC < ATC
→ ATC falls
MC = ATC
→ ATC is minimum
MC > ATC
→ ATC rises
Same logic applies to AVC also.
Super Important
MC cuts
ATC
at its minimum point.
MC cuts
AVC
at its minimum point.
One of the most repeated ICAI MCQs.
7. Shape of Cost Curves
Why U-Shape?
Phase 1:
Better efficiency leads to falling cost.
Phase 2:
Diminishing returns lead to rising cost.
Logic:
Same base logic as the law of production in the short run.
Curve
Shape
AFC
Always downward
AVC
U-shaped
ATC
U-shaped
MC
U-shaped
8. Long Run Cost
In the long run,
all costs are variable
.
There is
no fixed cost
in the long run.
Main concept tested here is
economies of scale
.
Types of Economies
Internal Economies
Better machinery
Specialisation
External Economies
Industry growth
Infrastructure development
Diseconomies
Management issues
Coordination problems
9. Shutdown Point
Definition
A firm continues production if
Price ≥ AVC
.
If
Price < AVC
, the firm should shut down.
Shutdown Point = Minimum AVC
Break-even Point = Minimum ATC
MCQ Gold Point
Shutdown point = minimum AVC
Break-even point = minimum ATC
10. Other Important Cost Types
1. Sunk Cost
Already incurred
Cannot be recovered
Should be ignored in decision making
2. Incremental Cost
Extra cost arising due to a change in decision or output.
3. Replacement Cost
Cost of replacing an existing asset.
4. Historical Cost
Original purchase cost of an asset.
MCQ Trap:
Historical cost is not necessarily relevant for present decision making.
Final Quick Revision
1-minute recall before the exam
Economic cost = Explicit + Implicit
Opportunity cost = next best alternative forgone
TC = TFC + TVC
AFC always falls
MC cuts ATC and AVC at the minimum point
Shutdown point = Price = AVC
Break-even point = Price = ATC
Sunk cost = ignore in decision making
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CA Foundation · Paper 4 · Business Economics · Unit 2: Theory of Cost
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