NPV and IRR Usually Agree. When They Do Not, Trust NPV.
Net present value and internal rate of return are the two standard tools for deciding whether an investment is worth making. They almost always point the same direction, but when they disagree, corporate finance has a clear answer for which one wins.
Two Ways to Ask the Same Question
When a company decides whether to build a new factory, launch a new product, or make an acquisition, it is really asking one question, will this investment create more value than it costs. Corporate finance has two standard tools for answering that question, net present value, commonly abbreviated NPV, and internal rate of return, commonly abbreviated IRR. Both tools use the same underlying idea, discounting, the practice of treating a dollar received in the future as worth less than a dollar in hand today, because that dollar could otherwise be earning a return elsewhere. Both tools, in the overwhelming majority of real business decisions, point to the same answer. But they are built differently, and in a specific set of situations they can disagree, and when they do, corporate finance has a clear, well established answer for which one to trust.
Net Present Value, the Straightforward One
Net present value takes every cash flow an investment is expected to produce, in every future year, and converts it into today's dollars using a discount rate, typically the company's cost of capital, the minimum return the company needs to earn to justify tying up money in the project instead of returning it to investors. Add up all those discounted future cash flows, subtract the upfront cost of the investment, and the result is the NPV. A positive NPV means the investment is expected to create more value than it costs, discounted for the time value of money and the riskiness of the cash flows. A negative NPV means the opposite. NPV's biggest strength is that it produces an answer in real dollars, this project is worth 4.2 million dollars more than doing nothing, which is directly comparable across projects of different sizes and directly useful for deciding whether a project is worth doing at all.
Internal Rate of Return, the Intuitive One
Internal rate of return asks a related but different question. Instead of picking a discount rate and calculating a dollar value, IRR calculates the discount rate at which the investment's NPV would equal exactly zero, in other words, the annualized rate of return the investment is expected to generate. An IRR of 18 percent means the project is expected to generate the equivalent of an 18 percent annual return on the capital invested. IRR is popular because it produces a single percentage that is easy to compare against a hurdle rate, the minimum acceptable rate of return a company sets for approving projects, and easy to compare intuitively against other opportunities, an 18 percent IRR sounds better than a 9 percent IRR the same way an 18 percent interest rate sounds better than a 9 percent one.
Where They Usually Agree
For a simple project, one upfront cost followed by a stream of positive cash flows, NPV and IRR will always agree on whether to accept or reject the investment. If the project's IRR is above the company's hurdle rate, its NPV at that hurdle rate will be positive, and vice versa. This is true for the vast majority of everyday corporate investment decisions, buying a new machine, opening a new store, launching a product with a conventional cost and revenue profile, which is exactly why most companies use both metrics side by side without worrying about a conflict.
Where They Disagree, and Why
The disagreement shows up in two specific situations. First, when comparing two mutually exclusive projects of different sizes, a small project can have a very high IRR but a small NPV, while a larger project has a lower IRR but a much larger NPV in dollar terms. Imagine choosing between a 100,000 dollar project with a 40 percent IRR and a 500,000 dollar project with a 20 percent IRR. The first project sounds more impressive as a percentage, but the second one likely creates far more actual value if a company has 500,000 dollars available to deploy and no better use for the rest of it. Second, when a project has unconventional cash flows, for example a large cost at the very end of the project's life, like an environmental cleanup or a decommissioning cost, the IRR calculation can produce multiple mathematically valid answers or no sensible answer at all, a known limitation that does not affect NPV, since NPV simply adds up discounted cash flows regardless of their pattern.
IRR tells you how efficient a dollar was. NPV tells you how much richer the company actually gets. When the two disagree, richer wins, which is why corporate finance treats NPV as the primary decision rule and IRR as a useful secondary check.
A Worked Example
A company has 600,000 dollars of capital available and a 10 percent cost of capital. It is choosing between two mutually exclusive projects.
| Project | Upfront cost | IRR | NPV at 10% |
|---|---|---|---|
| Project A | 100,000 | 35% | 28,000 |
| Project B | 600,000 | 18% | 96,000 |
Project A has the far more impressive IRR, 35 percent against 18 percent. But Project B creates more than three times as much actual dollar value, 96,000 dollars against 28,000 dollars, because it puts far more capital to work at a return still comfortably above the 10 percent cost of capital. A company with 600,000 dollars available and no better alternative use for the remaining 500,000 dollars should choose Project B. Choosing Project A on IRR alone and leaving the rest of the capital idle, or deployed at a lower return elsewhere, would leave real value on the table.
The Bottom Line
NPV and IRR almost always point the same direction, and using both is good practice. But when they conflict, usually because of project size differences or unusual cash flow patterns, NPV wins, because NPV answers the question that actually matters to a company's owners, how much richer does this decision make us.