Modified Internal Rate of Return (MIRR)

What Is Modified Internal Rate of Return (MIRR)?

Modified internal rate of return, or MIRR, is a project-return measure that adjusts the traditional internal rate of return by using separate assumptions for financing costs and reinvestment returns. It is designed to address common IRR problems, especially unrealistic reinvestment assumptions and multiple IRRs from unconventional cash flows.

MIRR is used in capital budgeting, private investment analysis, real estate, and project finance when cash flows occur at different times. It turns the project into a single annualized return, but it makes the reinvestment and financing assumptions more explicit than ordinary IRR.

MIRR Formula

A common expression is:

Positive cash flows are compounded forward to the end of the project at the reinvestment rate. Negative cash flows are discounted back to the start at the finance rate. The ratio is then converted into an annualized return over n periods.

Why MIRR Exists

Traditional IRR finds the discount rate that makes NPV equal zero. That can be useful, but it has two practical weaknesses. First, it can imply that interim cash flows are reinvested at the IRR, which may be unrealistic if the IRR is very high. Second, projects with cash flows that change sign more than once can produce multiple IRRs or confusing results.

MIRR forces the analyst to specify more plausible rates. The finance rate can reflect borrowing cost or cost of capital for outflows. The reinvestment rate can reflect what interim cash inflows can realistically earn.

Example

Suppose a project requires an initial investment, produces cash distributions along the way, and then requires a cleanup or reinvestment outflow near the end. Traditional IRR may struggle because cash-flow signs change more than once. MIRR discounts the outflows at the finance rate and compounds the inflows at the reinvestment rate, producing one cleaner annualized return.

The result may be lower than the headline IRR when the original IRR assumed reinvestment at an unrealistically high rate. That lower figure can be more useful for comparing projects.

MIRR Versus IRR

How to Use It

MIRR is most useful when comparing projects with irregular cash flows or when the ordinary IRR looks too attractive because of early distributions. It can also help investment committees show the reinvestment assumption directly rather than burying it inside a spreadsheet output.

The measure does not solve every problem. A small project can have a high MIRR while creating little total value. A large project with a lower MIRR may create more wealth. Risk, optionality, liquidity, taxes, leverage, and project size still matter.

A practical MIRR review should disclose the finance rate, reinvestment rate, timing convention, and cash-flow exclusions. Two analysts can produce different MIRR figures from the same project if one assumes reinvestment in low-risk cash instruments and another assumes redeployment into similarly risky projects. The number is most credible when the assumptions match the investor's actual opportunity set.

The Bottom Line

Modified internal rate of return is a cleaner version of IRR for many real-world cash-flow patterns. It improves the reinvestment assumption and avoids some multiple-rate problems, but it is only as good as the finance and reinvestment rates chosen.