Build Project Cash Flows for Interviews: Incremental, Sunk & Opportunity Costs
The biggest misconception in project finance is that a project cash flow is just the accountant's profit forecast with a discount rate attached. It is not. A CFO evaluating a new plant cares about only one brutal question: what cash will change because we say yes?
- Project cash flow is incremental: compare cash flows with the project versus without the project.
- Sunk costs are ignored: money already spent, such as feasibility studies, cannot be recovered and should not affect the decision.
- Opportunity costs are included: using an owned asset still has a cost if it could be rented, sold or used elsewhere.
- Include tax effects: depreciation is not a cash flow, but it creates a tax shield that affects cash flow.
- Working capital matters: extra inventory and receivables are cash outflows initially, usually recovered at the end.
- Financing costs stay out of project cash flows: interest is captured in the discount rate, not deducted again in free cash flow.
- Decision rule: accept if NPV > 0, assuming risk and strategic fit are acceptable.
The Big Picture: Project Cash Flow Is a Difference, Not a Forecast
Capital budgeting is not about listing every rupee connected to a project. It is about filtering the numbers into relevant cash flows: cash flows that arise only because the project is accepted.
Core Explanation: The Three Questions That Build the Cash Flow
A strong project cash flow model asks three questions in order.
The clean finance format is:
Free cash flow to the firm = EBIT × (1 - tax rate) + depreciation - capital expenditure - change in net working capital
This is before interest. If you deduct interest here and also discount at WACC, you double-count financing cost.
The Relevant Cost Map: Include, Ignore or Adjust
Most mistakes happen because candidates remember the labels but not the logic. Use this map.
The Cash Flow Build Cycle
Project cash flow modelling is rarely a straight line. You build, test, revise and return to the assumptions until the decision is robust.
A Small Worked Example: Building the Cash Flows End to End
Suppose a company is evaluating a three-year packaging line. The feasibility study already cost ₹5 lakh. That ₹5 lakh is a sunk cost and must be ignored.
Assumptions:
- Machine cost at time zero = ₹90 lakh
- Initial net working capital = ₹12 lakh, fully recovered at the end
- Annual revenue = ₹78 lakh
- Annual cash operating cost = ₹38 lakh
- Straight-line depreciation = ₹30 lakh per year for 3 years
- Tax rate = 25%
- Salvage value at the end = ₹10 lakh; book value is zero, so tax on salvage = ₹2.5 lakh
- Discount rate = 12%
So the project cash flows are:
The NPV is slightly positive, so financially the project clears the hurdle. But because the margin is thin, a manager should stress-test volume, price, raw material cost and salvage value before approving.
Definitions You Should Be Able to Say in One Breath
- Incremental cash flow: cash flow that occurs because a project is accepted, compared with not accepting it.
- Sunk cost: a past cost that has already been incurred and cannot be changed by the current decision.
- Opportunity cost: the cash benefit forgone by using a resource in this project instead of its next best use.
- Net working capital: current operating assets minus current operating liabilities needed to run the project.
- Depreciation tax shield: tax saving created because depreciation reduces taxable income.
- Terminal cash flow: after-tax cash flow from asset sale, working capital recovery and closure effects at project end.
Project Evaluation Metrics: What to Track
Once cash flows are built, the decision is evaluated using capital budgeting metrics. These are not interchangeable; each answers a different managerial question.
Case Study: Dixon Technologies and Capacity Expansion under Electronics Manufacturing
Dixon's contract manufacturing expansion shows why project cash flows must capture incremental volumes, working capital intensity, customer concentration, incentives and opportunity costs - not just plant capex.
Dixon Technologies, one of India's prominent electronics manufacturing services players, has grown by adding manufacturing capacity across categories such as mobiles, consumer electronics and appliances. In a business like this, the headline investment in new lines is only the visible part of the capital budgeting decision.
Situation: India's electronics manufacturing ecosystem has been supported by domestic demand, global supply chain diversification and government production-linked incentive schemes. For a contract manufacturer, growth often requires investing ahead of confirmed revenue: plant capacity, machinery, quality systems, vendor development and working capital.
The move: A capacity expansion decision would be evaluated through incremental project cash flows. The primary driver is expected incremental order volume from customers. Supporting drivers include operating efficiency from scale, eligibility for manufacturing incentives where applicable, customer pipeline visibility, supplier terms, yield improvement, and the ability to redeploy or upgrade lines if a product cycle changes.
The lesson: The project is not approved because “electronics manufacturing is growing.” It is approved only if the incremental after-tax cash flows, including working capital and opportunity cost of capacity, justify the investment under realistic downside scenarios.
So what: In high-growth manufacturing, the best answer is not “invest because demand is rising.” The best answer is “invest if the incremental cash flows survive customer, margin, working-capital and terminal-value stress tests.”
How AI Changes Building Project Cash Flows
AI does not remove finance judgement. It changes the speed and depth of assumption building.
- Driver extraction from documents: AI can summarize capex plans, segment commentary, order book language, raw material risks and working capital patterns from annual reports, investor presentations and credit rating reports.
- Scenario generation: AI tools can quickly generate downside cases such as lower utilization, delayed ramp-up, higher receivable days or lower salvage value. The finance professional still decides which assumptions are credible.
- Model review: AI can flag common modelling errors such as including sunk costs, deducting interest inside free cash flow, forgetting terminal working capital recovery or mixing nominal cash flows with real discount rates.
Use NotebookLM or ChatGPT like an analyst assistant: upload a company annual report, an investor presentation and your project assumptions, then ask, “List the incremental, sunk and opportunity cost items I should include or exclude in a capital budgeting model for this expansion.” Verify every number manually before using it.
Interview Relevance
“A company has spent ₹20 lakh on market research for a new product and now needs ₹5 crore to launch it. How will you build the project cash flows, and will you include the research cost?”
If the interviewer gives you an accounting profit statement, politely convert it into cash flow: add back depreciation, adjust for tax, remove interest, and include working capital and terminal cash flows.
Common Mistake
The most common mistake is treating every cost “related to the project” as relevant. This kills answers because it mixes sunk costs, allocated overheads and financing charges into the cash flow. Fix: ask one line for every item - “Will this cash flow change if we accept the project?”
What to Revise Next
Once you can build project cash flows, revise the discount rate used to value them. Move next to Cost of Equity, Cost of Debt & Calculating the Cost of Capital, then connect it to Capital Structure Theory: Irrelevance, Trade-Off & Pecking Order. Together, these topics explain both sides of capital budgeting: the cash flows and the rate used to discount them.