Capital allocation and investment appraisal is a senior management team’s most fundamental responsibility, but it is easy to overstate prospective rates of return. Cormac Lucey explains.

The goal of corporate investment should be to convert inputs – including money, things, ideas, and people – into something more valuable than they would otherwise be. After ten years in the position, a CEO whose company invests 10% of its existing capital stock each year will have been responsible for deploying more than half of all the capital at work in the business. This makes capital allocation and investment appraisal a senior management team’s most fundamental responsibility.

In financial terms, that means that investments should generate an after-tax rate of return greater than the company’s cost of capital. Management will generally use Discounted Cash Flow (DCF) analysis to test whether a project is likely to achieve this goal. Two specific DCF measures can be estimated.

If a company’s cost of capital is 7%, its investments need to generate a rate of return of at least 7% to adequately compensate investors for the risk they are exposing themselves to by investing in a company of that particular size, operating in that particular country, and in that particular sector. If the investment generates an 8% return, value is created. If the investment generates a 6% return, value is destroyed. By discounting projected future cash flows into their equivalent present values using the corporate cost of capital, net present value (NPV) quantifies the boost to shareholder value that an investment should generate.

The other key DCF measure is the Internal Rate of Return (IRR). For any given set of project cash flows, IRR quantifies the cost of capital that would generate a nil NPV. The IRR measures the average annual rate of return that the project expects to generate over its life. If a project’s IRR exceeds the cost of capital, it will be expected to boost shareholder value. But there is an assumption implicit in DCF mathematics, which can lead to IRR significantly overstating a project’s prospective rate of return.

The IRR approach assumes that intermediate project cash flows generated by the project (i.e. those generated after the initial investment period and before the project’s end) are themselves reinvested to generate a rate of return equal to the project’s IRR. If a company’s cost of capital is 7% and the project’s rate of return is 14%, this assumption means that surplus cash flows generated mid-project are themselves expected to be reinvested and to generate a 14% rate of return. This assumption is questionable: why should returns on surplus cash be higher just because they were generated by a high-return project?

Modified Internal Rate of Return (MIRR) applies exactly the same approach to evaluating a project as IRR, except it assumes that intermediate project cash flows generate a rate of return equal to the cost of capital (rather than the project’s IRR) when reinvested. This will generally be a more realistic assumption than that underpinning IRR. Having already calculated IRR, it is a simple matter to estimate a project’s MIRR using Excel’s ‘=MIRR’ function. The difference in the measured rate of return between IRR and MIRR can be significant. Consider a simple example.

Suppose we invest €1,000 today, and it is expected to generate annual after-tax cash flows of €140 for each of the next ten years, after which the project ends and we get our €1,000 investment back. The IRR of this project is 14%. But, if our cost of capital is 7%, the MIRR of the same projected cash flows would only be 11.4%.

Bottom line: IRR can systematically overstate prospective project returns with its unrealistic reinvestment rate return assumption. MIRR corrects this.

Cormac Lucey is an economic commentator and lecturer at Chartered Accountants Ireland.