Author: Taylor Warfield, Former Bain Manager and interviewer

Last Updated: July 18, 2026

 

A capacity expansion case interview asks you to decide whether a company should add capacity, when to add it, and how much, by linking a demand forecast to the capital expenditure, utilization, and risk involved. This guide gives you a clear 5-step method, two fully worked examples with the math, a comparison to related case types, and the seven mistakes that cost candidates the offer.

 

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Key Takeaways

 

A capacity expansion case is solved by forecasting demand, sizing the gap against current capacity, testing whether the investment pays back, and weighing the risk of overbuilding.

 

• These cases ask if, when, and how much to expand, not simply whether more capacity would be nice to have

 

• Start with the objective, then forecast demand, then size the capacity gap before touching any numbers

 

• The economics come down to comparing upfront capital expenditure against the extra contribution the new capacity earns

 

• Utilization risk is the core danger: capacity is mostly fixed cost, so weak demand erodes returns fast

 

• Phased or modular expansion is often the safest answer because it adds capacity in step with demand

 

What Is a Capacity Expansion Case Interview?

 

A capacity expansion case interview is a strategy case where you advise a company on whether to add production, service, or infrastructure capacity. You decide if the investment is justified, when to make it, and how large it should be, by comparing forecasted demand against current capacity and testing whether the returns beat the cost and risk.

 

These cases sit where operations meets strategy. The decision is forward-looking and hard to reverse, which is why interviewers like them: building a plant or opening a new facility commits real money for years. They want to see whether you can make a high-stakes call when the demand forecast is uncertain.

 

Capacity expansion is a specific flavor of the broader operations case interview, where the question centers on physical or service throughput rather than cost cutting or process redesign. The core tension is always the same: more capacity captures more demand, but it also locks in fixed cost that hurts if demand falls short.

 

On its careers site, McKinsey describes the case as a discussion of a real client scenario, which is exactly the spirit of a capacity decision. You are role-playing the consultant who has to tell a CEO whether to spend the money.

 

When Do Capacity Expansion Cases Show Up?

 

You get a capacity expansion case when a business is bumping against its operational limits and has to decide how to support future growth. The tell is almost always demand pressing on, or about to exceed, what the company can currently produce or serve.

 

Common triggers you should listen for include:

 

• Demand consistently runs above current capacity, or is forecast to

 

• Stockouts, long wait times, or lost sales trace back to capacity limits

 

• Utilization sits so high that the business cannot absorb a demand spike

 

• A growth plan on the table requires new plants, equipment, staff, or infrastructure

 

These cases cluster in capital intensive industries where capacity is expensive and slow to add. The table below shows where they appear most and what capacity actually means in each setting.

 

Industry	What capacity means	Typical trigger
Manufacturing	Plant lines, machines, factory floor space	Orders exceed what the plant can produce
Airlines and transport	Aircraft, routes, seats, fleet size	Routes sell out and load factors stay high
Hospitals and healthcare	Beds, operating rooms, clinicians	Occupancy near 100% turns patients away
Logistics and warehousing	Warehouses, trucks, sortation capacity	Volume growth overwhelms the network
Digital platforms	Servers, data centers, compute	Usage growth strains response times

 

Across these settings, BCG frames its case interview as working through a realistic business challenge step by step. A capacity decision is one of the cleanest versions of that, because the math and the judgment are both on display.

 

How Do You Structure a Capacity Expansion Case?

 

The best structure links five questions in a single chain: objective, demand, capacity gap, economics, and risk. Each step feeds the next, so by the end you reach a defensible recommendation rather than a pile of disconnected buckets.

 

1. Clarify the objective: confirm what success means here, whether that is profit, service level, or market share, and pin down the time horizon, because the test for whether to expand shifts with the goal
   
   
2. Forecast demand: project demand using growth rates, peak versus average load, and a range of scenarios rather than a single point estimate
   
   
3. Size the capacity gap: compare projected demand against current capacity to find when the company runs short and by how much
   
   
4. Test the economics: weigh the upfront capital expenditure and added fixed costs against the extra contribution the new capacity earns, then check the payback period or return
   
   
5. Weigh the risk: pressure-test what happens if demand disappoints, since unused capacity is mostly sunk fixed cost

 

Unlike a memorized template, this chain adapts to the prompt, which is what strong case interview frameworks are supposed to do. Tailor each step to the specific client, and tie every branch back to the objective you confirmed at the start.

 

Step four is where the numbers live, so clean case interview math matters more here than in most case types. You will be sizing demand, converting it into units of capacity, and comparing a one-time investment against a recurring stream of profit.

 

Do not forget the peak versus average distinction. A business may need enough capacity to cover peak periods even if that means idle capacity the rest of the year, and that gap between peak and average often drives how much you build.

 

Operational constraints round out the structure. Construction lead times, permits, workforce availability, and supply chain limits can all delay an expansion or cap how fast capacity comes online, so factor them into both timing and risk.

 

Structuring cases this way takes reps to make automatic. If you want to learn the method quickly, my case interview course walks you through proven structures in as little as 7 days.

 

Worked Example: Should the Company Expand, and by How Much?

 

Let's walk through a numerical version step by step. The numbers here are illustrative round figures chosen to make the math clean, not real company data.

 

Example: a packaged-food maker runs one plant with capacity for 100 million units per year. Current demand is 95 million units, so the plant runs at 95% utilization, and demand is growing 8% per year. Each unit sells for $2 with a variable cost of $1.20, leaving a contribution margin of $0.80 per unit.

 

First, forecast demand and find the gap. Next year demand reaches about 102.6 million units, which already tops the 100 million ceiling. By year three, demand grows to roughly 119.7 million units, so without expansion the company would leave nearly 19.7 million units of demand unserved that year.

 

That lost demand has a price. At $0.80 of contribution per unit, the roughly 19.7 million units of unmet demand in year three represent about $15.8 million in profit left on the table in a single year.

 

Now test the economics of a fix. Say the company can add a line that lifts capacity by 50 million units for $30 million upfront. The incremental contribution it earns builds each year: about $2.1 million in year one, $8.6 million in year two, and $15.8 million in year three, totaling roughly $26.5 million by the end of year three.

 

That puts the payback at a little over three years, which a simple breakeven analysis confirms is comfortably inside a normal plant investment horizon. The recommendation is to expand, but phase the build if possible and confirm the 8% growth assumption, since the entire case rests on it.

 

Worked Example: Build a New Plant or Expand the Existing One?

 

A second common version hands you two ways to add the same capacity and asks which is better. Again, the figures below are illustrative.

 

Example: a manufacturer is at 100% capacity at its only plant and needs 40 million units of additional annual capacity. Option A expands the existing plant for $40 million and comes online in 12 months. Option B builds a second plant near a fast-growing demand region for $50 million but takes 24 months.

 

On capital cost alone, Option A looks cheaper by $10 million. The trap is stopping there, because the two options differ on more than the sticker price.

 

The second plant sits closer to where new demand is growing. Say it cuts shipping cost by $0.15 per unit on those 40 million units, which is $6 million in savings every year. That extra $10 million of capital pays for itself in under two years through lower distribution cost.

 

Option B also spreads risk across two sites instead of concentrating everything in one, and it serves the growth region directly. The recommendation is to build the new plant if the regional demand is confirmed and the longer 24-month lead time is acceptable, otherwise expand the existing plant to capture demand faster.

 

How Is a Capacity Expansion Case Different From Other Case Types?

 

Capacity expansion overlaps with several case types but answers a narrower question: given demand we already understand, should we add capacity to serve it? The table below shows how it differs from the cases it is most often confused with.

 

Case type	Core question	How it differs
Capacity expansion	Should we add capacity, when, and how much?	Demand is roughly known, focus is the investment and risk
Market entry	Should we enter a new market, and how?	Demand is unknown and must be sized from scratch
Growth strategy	What is the best way to grow?	Considers every lever, not just adding capacity
Profitability	Why are profits falling and how do we fix it?	Diagnostic and backward-looking, not an investment call
Mergers and acquisitions	Should we buy this company?	Adds capacity by purchase, with fit and synergies in play

 

A market entry case interview forces you to size demand in a market the company does not serve yet. Capacity expansion starts from demand the company already sees and asks only how to supply more of it.

 

A growth strategy case interview is broader still, weighing pricing, new products, new geographies, and acquisitions side by side. Adding capacity is just one of the levers that case would put on the table.

 

A profitability case interview looks backward to explain why profits dropped, while capacity expansion looks forward to support growth. One is a diagnosis, the other is an investment decision.

 

The closest cousin is the merger and acquisition case, since buying a competitor is one way to add capacity. The difference is that an acquisition drags in questions of cultural fit, integration, and synergy that a greenfield build does not.

 

What Are the Most Common Capacity Expansion Case Mistakes?

 

Having coached hundreds of candidates one-on-one, I see the same errors sink capacity cases again and again. Avoid these seven and you will already be ahead of most of the field.

 

• Jumping to yes: recommending expansion before forecasting demand or confirming the objective

 

• Treating demand as certain: using a single number instead of a scenario range

 

• Ignoring peak versus average: missing the gap that often decides how much capacity to build

 

• Forgetting fixed cost: overlooking that idle capacity quietly destroys returns

 

• Leaving risk for the end: tacking it on in the last 30 seconds instead of weighing it in every step

 

• Skipping operational limits: ignoring lead times, permits, or staffing that delay the build

 

• Ending with it depends: refusing to commit to a clear, defended recommendation

 

If you keep tripping over the same errors, targeted feedback is the fastest fix. My case interview coaching pairs you with a former Bain interviewer who can spot the patterns you cannot see on your own.

 

A capacity expansion case interview rewards the candidate who connects demand, capacity, economics, and risk into one clear decision rather than a pile of buckets. Build the five-step chain, run the numbers, and commit to a recommendation. The single most useful thing you can do now is practice the structure out loud with realistic case interview examples until it feels automatic.

 

Frequently Asked Questions

 

What is a capacity expansion case interview?

 

A capacity expansion case interview is a strategy case where you advise a company on whether to add production, service, or infrastructure capacity. You decide if the investment is justified, when to make it, and how large it should be by comparing forecasted demand against current capacity and testing whether the returns beat the cost and risk.

 

How do you structure a capacity expansion case?

 

Structure it as a chain of five linked questions: clarify the objective, forecast demand, size the capacity gap, test the economics, and weigh the risk. Each step feeds the next, so by the end you have a single defensible recommendation rather than a list of disconnected buckets.

 

What industries use capacity expansion cases?

 

Capacity expansion cases show up most in capital intensive or throughput limited industries. Common examples include manufacturing plants, airlines and transport, hospitals and healthcare, logistics and warehousing, and digital platforms facing server or compute limits.

 

Is a capacity expansion case the same as a market entry case?

 

No. A market entry case asks whether a company should enter a new market and how. A capacity expansion case assumes the market is already served and asks whether to add capacity to meet rising demand, focusing on demand forecasting, capital expenditure, utilization, and overbuilding risk.

 

Are capacity expansion cases common in consulting interviews?

 

They are less common than profitability or market sizing cases, but they appear regularly in manufacturing, transport, and operations heavy interviews. The underlying logic of demand versus capacity versus economics also shows up inside larger growth and investment cases, so the structure is worth learning.

 

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