The internal rate of return (IRR) is often used by managers and practitioners for investment decisions. Unfortunately, it has serious flaws: (1) multiple real-valued IRRs may arise; (2) complex-valued IRRs may arise; (3) the IRR is, in general, incompatible with the net present value (NPV) in accept/reject decisions; (4) the IRR ranking is, in general, different from the NPV ranking; (5) the IRR criterion is not applicable with variable costs of capital. The efforts of economists and management scientists in providing a reliable project rate of return have generated over the decades an immense bulk of contributions aiming to solve these shortcomings. This article offers a complete solution to this long-standing unresolved issue by changing the usual perspective: the IRR equation is dismissed and the evaluator is allowed to describe the project as an investment or a borrowing at his discretion. This permits showing that any arithmetic mean of the one-period return rates implicit in a project reliably informs about a project's profitability and correctly ranks competing projects. With such a measure, which we call average internal rate of return, complex-valued numbers disappear and all the above-mentioned problems are wiped out. The economic meaning is compelling: it is the project return rate implicitly determined by the market. The traditional IRR notion may be found as a particular case.

This article shows that the internal rate of return (IRR) approach is unreliable and that the recently introduced average internal rate of return (AIRR) model constitutes the basis for an alternative theoretical paradigm of rate of return. To this end, we divide the paper into two parts: a pars destruens and a pars construens. In the “destructive” part, we present a compendium of 18 flaws associated with the IRR approach. In the “constructive” part, we construct the alternative approach from four (independent) economic intuitions and put the paradigm to the test by showing that it does not suffer from any of the flaws previously investigated. We also show how the IRR, as a rate of return, is absorbed into the new approach.

The Net Present Value maximizing model has a respectable ancestry and is considered by most scholars to be a theoretically sound decision model. In real-life applications, decision makers use the NPV rule, but apply a subjectively determined hurdle rate, as opposed to the ‘correct’ opportunity cost of capital. According to a heuristics-and-biases-program approach, this implies that the hurdle-rate rule is a biased heuristic. This work shows that the hurdle-rate rule may be interpreted as a fruitful strategy of bounded rationality, where several domain-specific and project-specific elements are integrated and condensed into an aspiration level. The paper also addresses the issue of a productive cooperation between bounded and unbounded rationality.