Plain definition
Internal rate of return, or IRR, is the discount rate at which the present value of a project’s future cash inflows equals its initial outflow, so net present value is zero. It expresses one possible return implied by a particular pattern of cash flows. Management often compares it with a required return, but the comparison is useful only after the cash flows and timing have been scrutinised.
IRR is not always available or decisive. Cash flows with more than one change of sign can produce multiple IRRs; some patterns have no meaningful IRR. A very high annualised IRR from a short project can also be less useful than its cash amount, scale, risk, and reinvestment assumptions. NPV usually remains clearer when choosing between mutually exclusive projects because it measures value in money.
Illustrative example
Monetary examples use Saudi riyals (SAR). The same principles apply in other currencies.
Suppose a project costs today and returns at the end of each of the next two years. Its IRR is about 13.1%: discounting the two receipts at about 13.1% brings them back to roughly . If the required return is 10% and the cash forecasts are credible, the project has positive NPV on that basis.
That result does not prove approval. A larger project with a lower IRR can create more value in SAR, and a two-month recovery can show a dramatic annualised IRR that says little about how the company will reinvest the money.
| Initial cash outflow | |
|---|---|
| Year-one receipt discounted at about 13.1% | |
| Year-two receipt discounted at about 13.1% | |
| Approximate NPV at IRR |
IRR uses cash-flow timing, not accounting profit. Do not rely on it without confirming the dates, signs, and whether cash flows are incremental.
Why it matters
A single percentage is easy to communicate, which is why teams can overuse it. Its limits matter most where capital is scarce, projects differ in scale, or the cash pattern is irregular—the very cases where an investment decision is hardest.
Practical consequence
Draw the cash-flow timeline before calculating IRR. Check whether there is one initial outflow followed by inflows; if not, inspect for multiple or missing solutions. Compare IRR with NPV at a documented required return, cash payback, scale, and execution constraints. Record the period used for annualisation and never present an extreme short-period rate as a normal annual business return.