What it means
Money now is worth more than the same money later. You could invest it, and there is always some risk that the future money never arrives.
NPV puts a number on that principle. It takes each expected future cash flow, shrinks it according to how far away it is and how risky it is, adds up those shrunken amounts, and compares the total with the upfront cost.
The shrinking is done with a discount rate. For a company, this is usually its cost of capital, the blended return that its lenders and shareholders require.
For an individual, it might be the return available on an alternative investment of similar risk. The discount rate is the single most important input, and small changes in it can flip a decision, which is why the worked example below shows the same project at two different rates.
NPV has real advantages over simpler methods. Unlike payback period, it counts every cash flow, not just those up to the point the investment is recovered.
Unlike accounting rate of return, it works with cash rather than profit. Unlike IRR, it gives a direct answer in currency and handles unusual cash flow patterns without ambiguity.
When two methods disagree, finance theory says to trust NPV. Its limitation is that it is only as good as the forecasts behind it.
Estimating cash flows five or ten years out is inherently uncertain, and choosing a discount rate involves judgement. Good practice is to test the NPV under several scenarios rather than relying on a single point estimate.
In practice
Real-world examples.
Example
A property investor compares buying a rental unit (large outlay now, rental income for years, resale at the end) against leaving the money in bonds. NPV at the bond yield tells them whether the property beats the safe alternative.
Example
A software company weighs building a new feature: development cost up front, extra subscription revenue over five years. Discounted at its cost of capital, the NPV shows whether the feature is worth building.
Example
A city evaluates a toll bridge: construction cost now, toll revenue and maintenance for 40 years. Public projects often use a lower "social" discount rate, which raises the NPV of long-lived benefits.
Think of it
“NPV is like calculating whether a coupon book is worth buying. You estimate savings, adjust for when you'll use them, and compare to the purchase price.
Formula
Calculation
NPV = sum of [ Cash Flow in year t / (1 + r) to the power t ] minus Initial Investment
where r is the discount rate and t is the year in which each cash flow arrives.
Worked example. A company is considering a machine costing 100,000 that will generate 40,000 of cash per year for three years.
At a 10% discount rate:
- Year 1: 40,000 / 1.10 = 36,364
- Year 2: 40,000 / 1.21 = 33,058
- Year 3: 40,000 / 1.331 = 30,053
- Present value of inflows = 99,475
- NPV = 99,475 minus 100,000 = negative 525
At an 8% discount rate:
- Year 1: 40,000 / 1.08 = 37,037
- Year 2: 40,000 / 1.1664 = 34,294
- Year 3: 40,000 / 1.2597 = 31,753
- Present value of inflows = 103,084
- NPV = 103,084 minus 100,000 = positive 3,084
The same machine is marginally value-destroying at 10% and value-creating at 8%. This is why getting the discount rate right matters so much, and why a project with an NPV close to zero deserves more scrutiny rather than an automatic yes or no.Case study
Seen in the real world.
A packaging company had to choose between two machines. Machine A cost 250,000 and would save 75,000 a year for five years. Machine B cost 400,000 and would save 105,000 a year for six years.
At the company's 9% cost of capital, Machine A had an NPV of about 41,700 and Machine B about 71,000. Machine B won on NPV despite its higher price and slower payback (3.8 years versus 3.3), because it created more total value. The finance team also noted that Machine B's NPV stayed positive even if savings came in 15% below forecast, while Machine A's turned negative at that level, which reinforced the choice.
Watch out
Common mistakes.
- Using the wrong discount rate, for example the interest rate on a loan rather than the overall cost of capital. Understating the rate makes weak projects look good.
- Ignoring cash flows after the forecast period. Many projects have a residual or terminal value that should be included.
- Mixing nominal cash flows with a real discount rate, or the reverse. Keep inflation treatment consistent.
Questions
People also ask.
What does an NPV of zero mean?
The project earns exactly the required rate of return, no more and no less.
NPV or IRR, which should I use?
NPV. IRR can give multiple answers or mislead when comparing projects of different sizes. Use IRR as a supporting statistic.
Why not just use payback period?
Payback ignores the time value of money and everything that happens after the payback date.
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