Using Relevant Costs to Decide on Expansion or Contraction

A factory running below its full capacity faces a familiar question: should it expand production to use up that spare capacity, or is it cheaper to scale back and buy the extra units from an outside supplier? This “expand or contract” decision sits at the heart of relevant costing, a technique management accountants use to strip away noise and focus only on the numbers that actually change with the decision.

What “expand or contract” really means 🔗

Every production unit has a ceiling. Below that ceiling, a company can choose to expand its own output to meet rising demand, or it can contract internal production and rely more on external purchases. Neither choice is automatically right. The correct answer depends on comparing the cost of making an additional unit in-house against the cost of buying it from a supplier, while also accounting for what happens to existing fixed costs.

This is essentially a variation of the classic make-or-buy decision, except the trigger here is a change in volume rather than a one-off sourcing choice. A firm might already be manufacturing a component, but as demand grows, it must decide whether to expand the production line or contract that portion of output to a vendor instead.

The core principle: only future, differential costs count 🔗

Relevant costing rests on one rule: a cost matters to a decision only if it is a future cost that differs between the alternatives being compared. Relevant costs are defined as expenditures that will only be incurred if a specific decision is made, which is why historical or unavoidable expenses have no place in the analysis.

Applied to an expand-or-contract choice, this means direct material, direct labour, and variable overhead almost always matter, because they change directly with the volume produced. Costs that stay the same no matter which option is chosen, such as head-office salaries or depreciation already committed, should be left out of the comparison entirely.

Sunk costs and unavoidable fixed costs stay out 🔗

Money already spent on machinery, or fixed overheads that will continue regardless of the decision, are irrelevant. A common analytical mistake is loading these unavoidable costs onto the “make” or “expand” option, which unfairly makes internal production look more expensive than it actually is going forward.

Fixed costs versus variable costs in the expansion decision 🔗

Cost behaviour is central to this whole exercise. Variable costs move in step with production volume, while fixed costs stay constant within a given range of output. This distinction shapes how an expansion or contraction decision plays out.

If a factory has spare machine hours and idle labour, expanding production usually only adds variable costs, since the fixed costs of rent, supervision, and equipment are already being paid regardless of volume. In that situation, expansion looks attractive as long as the extra revenue covers the extra variable cost.

When fixed costs stop being fixed 🔗

Fixed costs are only fixed within what accountants call the relevant range. Once a business pushes production beyond existing capacity, it may need a new shift, additional supervisors, or even a new machine, and at that point, expanding output requires additional investment in fixed costs such as leasing or building another facility. Contraction has the mirror effect: once volume drops below a threshold, a plant or shift may no longer be needed, and the fixed costs tied to it become avoidable.

This is why a genuine expand-or-contract analysis always asks two questions: how much extra variable cost will the change in volume create, and will it push fixed costs into a new step?

Idle capacity and the hidden cost of doing nothing 🔗

Spare capacity is not free just because it looks unused on paper. A plant that has already allocated its fixed costs to current output can absorb extra production using only the additional direct costs required, which is why using idle capacity for expansion is usually cheaper than it first appears. But if that same idle capacity has an alternative profitable use, choosing to expand production with it carries an opportunity cost, since the business gives up whatever it could have earned from that alternative use.

This is a point students often miss: the true cost of using existing capacity is zero only when there is genuinely no better use for it. If the machine hours could instead run a more profitable product line, that forgone contribution must be factored into the expansion decision.

Working through a make-or-buy style example 🔗

Consider a company currently manufacturing 10,000 units of a component. Management is deciding whether to expand in-house output further or contract part of it out to a supplier quoting a fixed price per unit.

On a purely quantitative basis, buying looks marginally cheaper. But this comparison holds only if the ₹25 of fixed overhead is genuinely avoidable, meaning it would actually disappear if the company contracted this portion of production. If that fixed cost would continue regardless, it should be excluded, which would flip the decision back in favour of making the units in-house. This is precisely the kind of adjustment that separates a rigorous relevant-cost analysis from a superficial one, and it echoes the broader point that only avoidable costs and opportunity cost should count when comparing making versus buying.

Beyond the numbers: qualitative factors 🔗

No expand-or-contract decision should be made on cost figures alone. Quality control, delivery reliability, dependence on a single supplier, and the strategic value of keeping a capability in-house all matter, especially when the cost gap between the two options is small. A supplier offering an attractive price today might raise rates once a company has dismantled its own production line, leaving it with little bargaining power later. Businesses also need to think about flexibility. Contracting out during a demand dip is easy to reverse if the company retains some in-house capability, but a full shutdown of a production line is harder to restart if demand rebounds sooner than expected.

Why this matters in the Indian context 🔗

Capacity utilisation decisions are especially relevant for India’s manufacturing base, where small and medium enterprises play an outsized role. MSMEs account for roughly 35.4 percent of India’s total manufacturing output, and many of these units operate with limited working capital, making the choice between expanding a production line and outsourcing part of it a genuinely high-stakes call rather than an academic exercise. Getting the relevant-cost analysis right can be the difference between a healthy margin and an unprofitable expansion that ties up scarce capital in idle machinery.

Putting it all together 🔗

An expand-or-contract decision is never just about comparing a purchase price to a production cost. It requires identifying which costs will genuinely change, checking whether fixed costs will step up or down at the new volume, valuing any opportunity cost of idle capacity correctly, and weighing qualitative risks alongside the numbers. Skipping any of these steps risks a decision that looks sound on a spreadsheet but fails in practice.

What do you think? If a company’s fixed costs are unavoidable either way, does the make-or-buy comparison change your intuition about which option is truly cheaper? And how much weight should qualitative factors like supplier dependence carry against a small cost advantage?

References

1. https://www.accountingtools.com/articles/what-is-a-relevant-cost.html
2. https://corporatefinanceinstitute.com/resources/accounting/fixed-and-variable-costs/
3. https://www.albany.edu/~dc641869/Chapter04.htm
4. https://costandprofitability.com/methods/make-or-buy-relevant-costs/
5. https://www.pib.gov.in/PressReleaseIframePage.aspx?PRID=2034923