What it means
The measure rests on the idea that a dollar arriving in three years is worth less than a dollar today, because today's dollar could be invested in the meantime. Discounting future cash flows at the company's cost of capital converts them into today's money, and the profitability index simply compares that total against the cash you have to put in at the start.
An index of 1.30 means every dollar invested generates $1.30 of value in present terms, or 30 cents of value creation per dollar committed. A result of exactly 1.0 means the project earns precisely the required return and no more, which is not a failure but is rarely worth the execution risk.
The measure earns its place when capital is limited and projects compete for it. Net present value tells you which single project adds the most value, but if you can only spend a fixed amount, ranking by profitability index tells you which combination gets the most out of every dollar available.
The mechanics are the same as a discounted cash flow calculation, so the answer is only as good as the inputs. The discount rate and the cash flow forecasts do most of the work, and shifting the discount rate by a couple of points can easily push a marginal project from above 1.0 to below it.
One variant subtracts the initial outlay from the numerator to give a net profitability index, where the break even point becomes zero rather than 1.0. Both versions rank projects identically, so the only thing that matters is being clear which one you are quoting.
In practice
Real-world examples.
Example
A hotel group ranks four refurbishment projects with indices of 1.45, 1.22, 1.08 and 0.94. With only enough capital for two, it funds the first two and rejects the fourth outright, since an index below 1.0 means the rooms would not earn back their cost of capital.
Example
A manufacturer compares a $2,000,000 line upgrade with an index of 1.15 against a $250,000 conveyor with an index of 1.60. The larger project adds more total value, so the board funds both rather than letting the ratio alone decide.
Example
A software firm reruns its profitability index at a 14% discount rate instead of 10% after borrowing costs rise. Two projects that scored 1.10 fall below 1.0, and the investment committee postpones them for a year.
Think of it
“The profitability index is like comparing investment returns per dollar. An investment returning $1.25 for every $1 invested beats one returning $1.10.
Formula
Calculation
Profitability index = present value of future cash flows / initial investment
A packaging business is considering a $500,000 machine with a cost of capital of 10%. It forecasts cash inflows of $220,000 in year one, $242,000 in year two and $266,200 in year three.
Discounting each year gives $220,000 / 1.10 = $200,000, then $242,000 / 1.21 = $200,000, then $266,200 / 1.331 = $200,000. The present value of future cash flows is $200,000 + $200,000 + $200,000 = $600,000, so the profitability index is $600,000 / $500,000 = 1.20. Every dollar invested returns $1.20 in today's money, and the equivalent net present value is $600,000 - $500,000 = $100,000.Case study
Seen in the real world.
This is an illustrative and fictional scenario. Calderwood Foods, an invented ready meal producer, had a capital budget of $1,200,000 and five competing proposals totalling $3,400,000. Historically the biggest requests won, on the reasoning that they came from the biggest departments.
The fictional finance team calculated a profitability index for each proposal using a 12% cost of capital. A $900,000 freezer expansion scored 1.08, while a $300,000 packaging line and a $250,000 energy recovery unit scored 1.55 and 1.62 respectively, and two smaller requests came in below 1.0.
Calderwood funded the packaging line, the energy unit and a $600,000 slice of a fourth project, spending its full budget on the highest value per dollar rather than on the loudest voice. In this illustrative case the change of ranking method added an estimated $340,000 of net present value from exactly the same amount of capital.
Watch out
Common mistakes.
- Ranking projects by profitability index when capital is not actually constrained, which can lead a business to reject a large value adding project in favour of a small efficient one.
- Forgetting to include ongoing costs and working capital in the cash flow forecasts, which inflates the numerator and makes weak projects look acceptable.
- Applying one company wide discount rate to projects with very different risk, so risky ventures are quietly flattered and safe ones penalised.
Questions
People also ask.
What does a profitability index of 1.0 actually mean?
It means the project earns exactly the required return, creating no extra value, so most boards treat it as a rejection unless there are strategic reasons to proceed.
How does it differ from net present value?
Net present value gives an absolute dollar amount of value created, while the profitability index expresses the same information as value per dollar invested.
Which discount rate should be used?
Normally the weighted average cost of capital, adjusted upwards when a project carries clearly higher risk than the rest of the business.
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