NPV and the Discount Rate: Why the Same Project Can Pass or Fail
October 21, 2026
Net present value (NPV) discounts future cash flows back to today and subtracts the initial investment. A project that costs $1,000 and returns $400 a year for three years has an NPV of +$30.84 at an 8% discount rate, but −$5.26 at 10%. The decision flips because the project's internal rate of return (IRR) is about 9.7%.
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NPV = −1,000 + 400/(1+r) + 400/(1+r)² + 400/(1+r)³. At 8%, the discounted cash flows are 370.37, 342.93, and 317.53, which add up to 1,030.84, leaving NPV = 30.84. At 10%, they are 363.64, 330.58, and 300.53, totaling 994.74, so NPV = −5.26.
With no discounting the cash flows sum to $1,200, a $200 gain. Discounting at higher rates removes more and more of that.
| Discount rate | NPV | Decision |
|---|---|---|
| 0% | +$200.00 | Accept |
| 8% | +$30.84 | Accept |
| 9.7% (IRR) | $0.00 | Indifferent |
| 10% | −$5.26 | Reject |
| 12% | −$39.27 | Reject |
Where the Rate Comes From
The discount rate represents the return you could earn elsewhere on investments of similar risk, called the opportunity cost of capital. Companies often use their weighted average cost of capital (WACC) and add a premium for riskier projects. Individuals might use the return on a comparable investment or the interest rate on debt they could pay off.
Because NPV is so sensitive to the rate, test a range of values. A project that is acceptable only in a narrow band of rates is fragile.
Reading NPV and IRR Together
NPV tells you how much value a project adds in today's money, while IRR is the break-even rate. A positive NPV means the project's return exceeds the discount rate. Use NPV to rank mutually exclusive projects of different sizes, because IRR can favor small projects with high percentage returns over larger ones that create more total value.
Cash flow estimates are the weakest part of any NPV, so spend as much effort on realistic forecasts as on the math.
Frequently Asked Questions
What does a negative NPV mean?
The project earns less than the discount rate, so it would reduce value compared with the alternative investment.
How is the discount rate chosen?
Usually from the cost of capital or the return available on similar-risk alternatives.
What is the relationship between NPV and IRR?
IRR is the discount rate at which NPV equals zero.
Why does a higher discount rate lower NPV?
Future cash flows are worth less in today's money when the rate used to discount them is higher.