A regional manufacturer is deciding between two machines. Machine A costs 8,000,000 BDT and generates steady cash flows for six years. Machine B costs half as much and pays back faster, but tapers off after year three. The finance team runs both through payback period and calls it a day. Eighteen months later, the board asks why the "faster payback" machine actually destroyed value. This is the moment every finance professional eventually meets: the gap between a project that looks good and a project that is good.
That gap is exactly what Net Present Value (NPV) and Internal Rate of Return (IRR) exist to close. Both are core tools in capital budgeting, but here's the catch , they don't always agree with each other, and when they disagree, most analysts pick the wrong one for the wrong reason.
1. Why payback period and simple ROI fail as decision tools
2. NPV explained — the concept, the formula, and what it really measures
3. IRR explained — and why it quietly lies to you sometimes
4. Building both models step by step with a real example
5. When NPV and IRR disagree (and which one wins)
6. Common mistakes analysts make
7. Industry best practices
8. Advanced considerations: reinvestment rate, mutually exclusive projects, capital rationing
9. FAQs
Why the Traditional Approach Fails
Most junior analysts start with payback period — how many years until the initial investment is recovered. It's intuitive, easy to explain to a board, and almost completely blind to what happens after the payback point.
Consider two projects, each requiring a 5,000,000 BDT outlay:
| Year | Project A (Cash Flow) | Project B (Cash Flow) |
|---|---|---|
| 1 | 2,000,000 | 3,000,000 |
| 2 | 2,000,000 | 2,000,000 |
| 3 | 2,000,000 | 500,000 |
| 4 | 2,500,000 | 200,000 |
| 5 | 2,500,000 | 100,000 |
Payback period says Project B wins — it recovers the investment in year 2, versus year 3 for Project A. But Project A generates far more total cash over its life, and that cash arrives later, when compounding effects and terminal value matter more than a checklist metric can capture.
Here's why this matters: payback period ignores the time value of money and ignores everything that happens after the cutoff date. Simple ROI has the same blind spot — it treats a taka earned in year 1 the same as a taka earned in year 5. In a country like Bangladesh, where discount rates often sit well above 10-12% due to inflation and borrowing costs, that distortion is not cosmetic. It's material.
NPV: What It Actually Measures
NPV answers one question, and it answers it in currency, not in percentage: if I undertake this project, how much richer is the company today, in today's money?
where CFt = cash flow in year t, r = discount rate (cost of capital), t = year
Why does this matter to a CFO more than any other single number? Because NPV is additive across projects, it directly ties to shareholder wealth, and it never produces more than one answer for a given cash flow pattern. IRR, as you'll see, can produce zero, one, or several answers depending on how cash flows are shaped.
How Professionals Use NPV
In practice, corporate finance teams set a hurdle rate — often the weighted average cost of capital (WACC) plus a risk premium for project-specific uncertainty. Any project with a positive NPV at that hurdle rate clears the bar. A private equity fund evaluating a leveraged buyout, for instance, might use a 15-18% discount rate to reflect both the cost of debt and the return demanded by equity investors, then reject any target whose projected NPV comes in negative at that rate.
IRR: The Metric Everyone Loves, and Why That's a Problem
IRR is popular for one simple reason: it's a percentage, and percentages are easy to compare, communicate, and rank. "This project returns 22%" is a much easier boardroom sentence than "This project generates 4.2 million BDT of NPV at a 14% discount rate."
But IRR has two structural weaknesses that trip up even experienced analysts.
Problem 1: The Reinvestment Assumption
IRR implicitly assumes that every interim cash flow gets reinvested at the IRR itself. For a project yielding a 35% IRR, that means assuming you can reinvest each year's cash flow at 35% elsewhere in the business. That's rarely realistic. NPV, by contrast, assumes reinvestment at the more conservative and defensible cost of capital.
Problem 2: Multiple IRRs
When a project's cash flow pattern flips sign more than once — cash out, then in, then out again, as happens with projects requiring a major mid-life overhaul or decommissioning cost — the math can produce two or more valid IRRs. Which one is "correct"? None of them, reliably. This is common in mining, oil and gas, and any capital-intensive manufacturing line with a large end-of-life remediation cost.
Building the Model Step by Step
Let's return to the manufacturing example and build it properly. A textile company in Gazipur is evaluating a new dyeing line costing 8,000,000 BDT, with a useful life of 6 years and a cost of capital of 13%.
| Year | Cash Flow (BDT) | Discount Factor @13% | Present Value |
|---|---|---|---|
| 0 | (8,000,000) | 1.000 | (8,000,000) |
| 1 | 1,800,000 | 0.885 | 1,593,000 |
| 2 | 2,100,000 | 0.783 | 1,644,300 |
| 3 | 2,400,000 | 0.693 | 1,663,200 |
| 4 | 2,400,000 | 0.613 | 1,471,200 |
| 5 | 2,200,000 | 0.543 | 1,194,600 |
| 6 | 2,000,000 | 0.480 | 960,000 |
Step 1: Discount each cash flow. Multiply each year's cash flow by its discount factor (1 / (1+0.13)^t).
Step 2: Sum the present values. Adding the discounted cash flows above (excluding year 0) gives 8,526,300 BDT.
Step 3: Subtract the initial investment. NPV = 8,526,300 − 8,000,000 = 526,300 BDT. Positive NPV — the project clears the 13% hurdle and creates value.
Step 4: Solve for IRR. Using trial and error or a financial calculator, the discount rate that sets NPV to zero for this cash flow stream comes out to approximately 14.6%. Since 14.6% exceeds the 13% cost of capital, IRR agrees with NPV here — go ahead.
When NPV and IRR Disagree
Here's where many analysts make mistakes. When you're choosing between two mutually exclusive projects — you can only pick one — NPV and IRR can rank them differently. This typically happens when the projects differ significantly in scale or in the timing of their cash flows.
| Metric | Project X (Large plant expansion) | Project Y (Smaller efficiency upgrade) |
|---|---|---|
| Initial Investment | 20,000,000 BDT | 4,000,000 BDT |
| NPV @ 12% | 3,100,000 BDT | 1,450,000 BDT |
| IRR | 17% | 26% |
Project Y has the higher IRR. But Project X generates more absolute value. If capital is unconstrained, a company should choose Project X — it adds more wealth in taka terms, which is what shareholders actually care about. IRR's percentage framing makes Project Y look more attractive, but percentages don't pay dividends. Currency does.
Common Mistakes to Avoid
- Using the same discount rate for projects with very different risk profiles
- Ranking mutually exclusive projects purely by IRR
- Ignoring multiple IRR solutions in projects with non-conventional cash flow patterns
- Forgetting to include terminal or salvage value in the final year's cash flow
- Applying nominal discount rates to real (inflation-adjusted) cash flows, or vice versa
- Treating a positive NPV as approval without checking capital rationing constraints
Industry Best Practices
Large corporates typically run three numbers side by side: NPV at the base-case discount rate, IRR as a sanity check, and a sensitivity table showing NPV at discount rates one to two points above and below the base case. This last step matters more than most analysts realize — a project with a thin NPV cushion is fragile to even small changes in the cost of capital assumption.
Private equity firms often add a fourth lens: MOIC (multiple on invested capital), since IRR alone can be gamed by structuring deals with fast, small early distributions. A quick payout in year one can inflate IRR dramatically without meaningfully growing invested capital.
Advanced Considerations
Capital Rationing
When capital is limited — a common reality for SMEs and even mid-sized banks with lending caps — the profitability index (PI = present value of future cash flows ÷ initial investment) becomes more useful than raw NPV, because it ranks projects by value created per unit of capital deployed, not just total value.
Reinvestment Rate Realism
For long-duration infrastructure or public sector projects, always stress-test the reinvestment assumption. If interim cash flows can't realistically be redeployed at the calculated IRR, use MIRR with a reinvestment rate tied to observable market returns, such as the yield on government treasury bills.
Frequently Asked Questions
Is a higher IRR always better than a higher NPV?
No. IRR is a percentage measure of efficiency, while NPV is an absolute measure of value created. For mutually exclusive projects of different sizes, prioritize NPV.
What discount rate should I use for NPV?
Most companies use their weighted average cost of capital (WACC), adjusted upward for project-specific risk when the project is materially riskier than the company's existing operations.
Can NPV be negative and IRR still look attractive?
Yes, if the discount rate used in the NPV calculation is higher than what feels intuitive, or if cash flows are heavily backloaded. This is exactly why both metrics should be reviewed together, not in isolation.
What is a good IRR for a small business project in Bangladesh?
There's no universal number — it depends on the company's cost of capital and sector risk. As a rough anchor, many SMEs use a hurdle rate of 15-20% given local borrowing costs and inflation, but this should be calculated specifically for each business.
Conclusion: What to Do Next
Next time a capital budgeting decision crosses your desk, don't start with payback period and don't stop at IRR. Build the full discounted cash flow model, calculate NPV at your true cost of capital, cross-check with IRR, and run a sensitivity table across a realistic range of discount rates. If the two metrics disagree on a mutually exclusive choice, trust NPV — it's the one number that ties directly back to the wealth you're actually trying to create.
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