Understanding your profitability index
The table below summarizes how the profitability index is typically interpreted in capital-budgeting decisions, consistent with standard discounted cash flow analysis.
| PI range | Interpretation | Typical decision |
|---|---|---|
| PI > 1.0 | Present value of inflows exceeds the initial cost; positive NPV | Accept (value-creating at the given discount rate) |
| PI = 1.0 | Present value of inflows exactly equals the initial cost; NPV = 0 | Indifferent — breakeven at the given discount rate |
| PI < 1.0 | Present value of inflows is less than the initial cost; negative NPV | Reject (value-destroying at the given discount rate) |
- The profitability index depends heavily on the chosen discount rate; a rate that is too low will overstate a project's attractiveness and a rate that is too high will understate it.
- PI ranks efficiency per dollar invested well, but when comparing mutually exclusive projects of different scale, NPV and PI can occasionally disagree — most finance texts recommend NPV as the primary decision rule in that case.
- This calculator assumes all cash flows occur at the end of each period and uses a single constant discount rate throughout; it does not model changing rates or irregular timing.
What is the profitability index?
The profitability index is a capital-budgeting metric that expresses the present value of a project's expected future cash inflows as a ratio to the initial investment needed to start the project. It is mathematically related to net present value (NPV): PI = 1 + (NPV ÷ initial investment), so any project with a positive NPV will always show a PI above 1.0, and any project with a negative NPV will show a PI below 1.0.
Because it is expressed as a ratio rather than a dollar amount, the profitability index is particularly useful for comparing or ranking projects of different sizes, or for choosing among mutually exclusive projects when capital is limited (capital rationing). A small project with a high PI can be a more efficient use of a constrained budget than a larger project with a higher NPV but a lower PI.
The CFA Institute curriculum presents the profitability index alongside NPV and internal rate of return (IRR) as one of the standard discounted cash flow techniques used in capital budgeting to evaluate whether a prospective investment is expected to add value.
How to use this profitability index calculator
- Enter the initial investment — the upfront cash outlay required for the project, entered as a positive number.
- Enter the expected future cash flows, one per period, separated by commas, in the order they are expected to occur (period 1, period 2, and so on).
- Enter the discount rate — typically the project's cost of capital or a required rate of return — used to convert future cash flows into today's dollars.
- Read the profitability index, the present value of the inflows, and whether the project is classified as value-creating or value-destroying at the entered discount rate.
The formula behind the profitability index
Each future cash flow is discounted back to the present using the discount rate and the number of periods until it occurs, then all discounted values are summed to produce the total present value of inflows. Dividing that sum by the initial investment produces the profitability index.
A PI above 1.0 means the present value of the inflows exceeds the cost of the investment, implying the project is expected to create value at the given discount rate; a PI below 1.0 means the opposite. For example, cash flows of $3,000, $4,000, $5,000 and $6,000 discounted at 10% produce a present value of roughly $13,887.71 against a $10,000 initial investment, giving a PI of about 1.389.
Common mistakes
- Treating PI as the sole decision criterion when comparing projects of very different sizes — a smaller project can show a higher PI while creating less total dollar value than a larger project with a lower PI.
- Using an inconsistent or overly optimistic discount rate that does not reflect the project's actual risk or the true cost of capital.
- Forgetting that PI already incorporates the initial investment, so it should not be combined with a separate ROI calculation using the same cash flows without adjusting for double-counting.
- Ignoring the timing of cash flows — entering flows in the wrong order changes how much each is discounted and materially changes the resulting PI.
Perguntas frequentes
What does a profitability index of 1.5 mean?
A profitability index of 1.5 means the present value of a project's expected cash inflows is 1.5 times its initial investment cost — in other words, for every $1 invested, the project is expected to return $1.50 in discounted value. This corresponds to a positive net present value equal to 0.5 times the initial investment.
How is the profitability index different from NPV?
Net present value (NPV) reports the dollar amount of value a project is expected to create, while the profitability index expresses that same value as a ratio relative to the initial investment. PI = 1 + (NPV ÷ initial investment), so the two measures are mathematically linked and always agree on whether a single project is worth accepting.
What is a good profitability index?
Any profitability index above 1.0 indicates the project's discounted cash inflows exceed its cost at the chosen discount rate, which is generally the threshold for accepting a project under standard capital-budgeting rules. Higher values indicate more value created per dollar invested, which is especially useful when ranking projects under a limited capital budget.
Why would PI and NPV give conflicting rankings for two projects?
PI measures value created per dollar invested, while NPV measures total dollar value created. A small project can have a high PI but a low NPV, while a large project can have a lower PI but a higher total NPV — when the two rankings conflict for mutually exclusive projects, most corporate finance texts recommend using NPV as the primary decision rule since it directly measures added value.
Does the discount rate affect the profitability index?
Yes, significantly. Raising the discount rate reduces the present value of future cash inflows and therefore lowers the PI, while lowering the discount rate raises the PI. The discount rate should reflect the project's risk and the organization's cost of capital for the PI to be a meaningful decision input.
Referências
- CFA Institute. Capital Budgeting — CFA Program Curriculum, Corporate Finance and Equity readings. cfainstitute.org.
- U.S. Securities and Exchange Commission, Investor.gov. Discounted cash flow and investment analysis basics. investor.gov.
- Brealey RA, Myers SC, Allen F. Principles of Corporate Finance. 13th ed. McGraw-Hill Education.
- Damodaran A. Investment Valuation and Capital Budgeting. New York University Stern School of Business. pages.stern.nyu.edu/~adamodar.