Financial Valuation Methods in Case Interviews: NPV, IRR, and DCF

Financial valuation methods separate candidates who mechanically plug numbers from those who understand investment logic. Roughly 20-25% of consulting case interviews involve M&A, private equity, or strategic investment decisions where you need to assess whether a deal creates value. Based on our analysis of 800+ case interviews, the three core methods — NPV, IRR, and DCF — show up consistently, but interviewers rarely expect you to complete a full spreadsheet calculation. What they test is your understanding of the economic intuition, ability to estimate reasonable inputs quickly, and judgment about when each method applies.

The Three Core Valuation Methods

Each method answers a different business question. Mixing them up signals a fundamental gap in financial literacy.

Why These Three Matter in Cases

M&A cases, private equity investments, and capital allocation problems all require you to estimate whether future cash flows justify the investment today. The interviewer hands you a scenario — “Should we acquire this company for $500M?” or “Which of these three projects should we fund?” — and expects you to structure your analysis around one of these three methods.

In our experience coaching candidates, the strongest answers name the method explicitly: “This is an NPV problem because we’re evaluating a single go/no-go decision” or “I’ll use IRR to compare these three competing projects.” Weak answers jump straight into calculation without stating which valuation logic applies.

NPV: The Go/No-Go Decision Tool

Net Present Value calculates the total value created by an investment, expressed in today’s dollars. If NPV is positive, the investment returns more than the cost of capital and should proceed. If NPV is negative, it destroys value.

flowchart LR
    A[Investment Decision] --> B{Calculate NPV}
    B --> C[NPV > 0]
    B --> D[NPV < 0]
    C --> E["Invest\n(Value Created)"]
    D --> F["Pass\n(Value Destroyed)"]
    
    B --> G["Sum of PV(Cash Flows)"]
    G --> H["Discount Rate\n(WACC or Hurdle Rate)"]

NPV Formula and Logic

NPV = -Initial Investment + ∑ (Cash Flow_t / (1 + r)^t)

Where:

• r = discount rate (cost of capital or hurdle rate)
• t = time period (year 1, 2, 3, etc.)
• Cash flows are net inflows (revenue - costs)

Quick NPV Example

Scenario: A manufacturing plant expansion costs $10M upfront and generates $3M in annual cash flow for 5 years. The company’s hurdle rate is 10%. Should they invest?

Calculation shortcut: Rather than calculating each year separately, recognize this is an annuity. Use the annuity factor approximation:

• PV of $3M annuity at 10% for 5 years ≈ $3M × 3.8 = $11.4M
• NPV = -$10M + $11.4M = +$1.4M
• Decision: Invest — the project creates $1.4M in value

Common NPV Pitfalls in Interviews

IRR: Comparing Competing Investments

Internal Rate of Return is the discount rate that makes NPV equal zero — in other words, the break-even return rate. IRR is most useful when comparing multiple investment options or when you want to know what return you’re earning.

IRR Formula and Intuition

0 = -Initial Investment + ∑ (Cash Flow_t / (1 + IRR)^t)

You’re solving for IRR, the rate that equates the present value of inflows to the initial outlay.

Interpretation: If IRR > hurdle rate, the investment exceeds minimum return requirements. If IRR < hurdle rate, pass.

Practical IRR Example

Scenario: A tech startup wants to invest in three R&D projects. All cost $5M upfront. Which should they choose?

Analysis: Project B has the highest IRR at 25%, meaning it generates the best percentage return. If the company’s hurdle rate is 15%, all three clear the bar, but B creates the most value per dollar invested.

In an interview, you would say: “I’d recommend Project B because it delivers a 25% IRR, which not only exceeds our 15% hurdle rate but also offers the highest return among the three options. The front-loaded cash flows in Project C reduce reinvestment risk, but B’s total return outweighs that benefit.”

IRR Limitations

IRR has well-known weaknesses that strong candidates acknowledge:

1. Multiple IRRs: Projects with alternating cash flows (negative, positive, negative) can have multiple IRR solutions
2. Scale blindness: A project with 50% IRR on $1M investment may be worse than 20% IRR on $100M
3. Reinvestment assumption: IRR assumes you can reinvest interim cash flows at the IRR itself, which is often unrealistic

When to flag this in an interview: If the interviewer gives you a case with very different project sizes, say: “IRR alone may not be the best metric here because a smaller project with higher IRR could deliver less total value than a larger project. I’d also look at absolute NPV.”

DCF: Valuing an Ongoing Business

Discounted Cash Flow values a company by forecasting its future free cash flows and discounting them back to today. DCF is the foundation of most M&A valuations.

DCF Structure

flowchart TD
    A[DCF Valuation] --> B[Forecast Period\n5-10 Years]
    A --> C[Terminal Value\nYears Beyond Forecast]
    
    B --> D[Revenue Projections]
    B --> E[EBITDA Margin]
    B --> F[Capex & Working Capital]
    B --> G[Free Cash Flow]
    
    C --> H[Perpetuity Growth]
    C --> I[Exit Multiple]
    
    G --> J[Discount at WACC]
    H --> J
    I --> J
    
    J --> K[Enterprise Value]
    K --> L[Subtract Net Debt]
    L --> M[Equity Value]

DCF Building Blocks

Simplified DCF Example

Scenario: You’re valuing a software company. It generates $50M in EBITDA today, expected to grow 15% annually for 5 years, then 3% perpetually. Assume 10% WACC, 25% tax rate, and minimal capex.

Step 1: Forecast explicit period cash flows

Step 2: Calculate terminal value

• Year 6 FCF = $75.4M × 1.03 = $77.7M
• Terminal Value = $77.7M / (10% - 3%) = $1,110M

Step 3: Discount everything to present

• PV of explicit period ≈ $43.1M/1.1 + $49.6M/1.1² + … ≈ $220M
• PV of terminal value = $1,110M / 1.1^5 ≈ $690M
• Enterprise Value = $220M + $690M = $910M

In an interview, you’d present the logic: “Based on current EBITDA and a 15% growth assumption for five years, this company is worth roughly $900M on an enterprise value basis. About 75% of that value comes from the terminal period, which is typical for high-growth software companies. If we’re acquiring for $500M, this implies significant upside — but we’d want to stress-test the growth assumption and terminal multiple.”

Choosing the Right Method in a Case

The method you pick depends on the business question.

The Decision Tree

When the interviewer hands you an investment case:

1. Ask: “Are we valuing a business or a project?”

   • Business → DCF
   • Project → NPV or IRR

2. Ask: “Is this a go/no-go decision or a choice among options?”

   • Go/no-go → NPV
   • Choose among options → IRR (or NPV if scale matters)

3. Clarify inputs: “What discount rate should I use?” and “Do we have a terminal value assumption?”

Practical Shortcuts for Case Interviews

You will not have time to build a full spreadsheet. Use these mental shortcuts:

Annuity Factor Approximation

For equal annual cash flows, use annuity factors:

Example: $5M annual cash flow for 5 years at 10% = $5M × 3.8 = $19M present value

Terminal Value Quick Estimate

Perpetuity Method: Terminal Value = Year N+1 Cash Flow / (WACC - Growth Rate)

If growth rate = 3% and WACC = 10%, the denominator is 7%, or roughly 14-15× the final year’s cash flow.

WACC Approximation

For mature companies: WACC ≈ 8-12% For high-growth tech: WACC ≈ 10-14%

If the interviewer doesn’t give you WACC, propose a reasonable range and validate: “I’m assuming a 10% discount rate for a stable industrial company — does that align with your expectations?”

Common Valuation Mistakes to Avoid

Based on our work with candidates, these errors come up repeatedly:

1. Confusing enterprise value and equity value

   • Enterprise Value = Equity Value + Net Debt
   • In M&A, you buy the enterprise value, so subtract debt to get to equity value

2. Using EBITDA as a proxy for cash flow

   • EBITDA ignores taxes, capex, and working capital changes
   • Always adjust: FCF = EBITDA - Taxes - Capex - ΔWorking Capital

3. Forgetting to validate assumptions

   • A 20% perpetual growth rate is unrealistic (exceeds GDP)
   • Discount rates below 6% are too low for most businesses
   • Ask: “Does this assumption pass the smell test?”

4. Failing to state the decision clearly

   • Don’t end with “NPV is $5M” — say “NPV is positive $5M, so we should invest”

Integration with CasesCoach AI Mock Interview

Valuation methods require practice under time pressure, and traditional study methods don’t replicate the stress of calculating NPV or IRR while an interviewer watches. CasesCoach’s AI Mock Interview lets you practice these scenarios in two modes:

Guided Mode: The AI interviewer prompts you through each step — “What discount rate will you use?” “How are you calculating terminal value?” This mode helps you internalize the logic and catch errors in real time, building muscle memory for structuring valuation problems correctly.

Expert Mode: Simulates real interview pressure. You must structure the valuation approach, estimate inputs, and justify your assumptions without hints. The AI scores your performance across five dimensions — Structure, Analysis, Communication, Business Acumen, and Math — highlighting exactly where you lost points.

After each mock session, you receive detailed feedback on your valuation logic: Did you choose the right method? Were your assumptions reasonable? Did you articulate the business decision clearly? This beats solo practice because you see how an interviewer evaluates your approach in real time.

With 835+ real consulting cases in our library, you can practice valuation methods across M&A, private equity, strategic investment, and capital allocation scenarios. Free users get 3 complete cases plus one AI Mock trial. Pro members unlock unlimited access to the full case library and multiple AI Mock sessions to refine their valuation skills until they’re interview-ready.

Try AI Mock Interview for free or explore all pricing options.

Key Takeaways

• NPV answers “Should we invest?” — use it for go/no-go decisions on single projects
• IRR answers “What return do we earn?” — use it to compare multiple investment options
• DCF answers “What is this business worth?” — use it to value acquisition targets or ongoing companies
• Always state which method you’re using and why before diving into calculations
• In interviews, focus on the economic logic and business judgment, not calculation precision — interviewers care more about whether you understand why NPV is positive than whether you got the exact number
• Validate assumptions with the interviewer and flag when a method’s limitations (like IRR’s scale blindness) might affect the recommendation