MIRR Calculator
Calculate the modified internal rate of return for an investment using your finance and reinvestment rates.
What Is the Modified Internal Rate of Return?
The Modified Internal Rate of Return (MIRR) addresses a key limitation of the standard IRR calculation. Traditional IRR assumes that all positive cash flows generated by a project are reinvested at the project's own IRR, which is often unrealistically high. MIRR instead allows you to specify a realistic reinvestment rate for future cash flows and a separate finance rate for the initial investment outlay. This produces a more accurate and conservative measure of a project's profitability.
How the MIRR Calculation Works
The MIRR formula solves for the rate that equates the present value of costs (financed at the finance rate) to the future value of positive cash flows (compounded at the reinvestment rate). The calculation follows three steps:
- Discount negative cash flows to the present using the finance rate. This accounts for the cost of funding the investment.
- Compound positive cash flows forward to the end of the project using the reinvestment rate. This reflects what you could earn by reinvesting returns.
- Solve for the rate that equates the present value of costs to the future value of returns over the project's duration.
Because MIRR uses explicit rates for financing and reinvestment, it eliminates the multiple IRR problem and provides a single, unambiguous rate of return.
How to Use the MIRR Calculator
Enter your cash flow series as a comma-separated list. The first value represents the initial investment (typically a negative number). Subsequent values represent net cash flows for each period. Then set your finance rate and reinvestment rate as percentages.
- Cash Flows: Enter each period's net cash flow, separated by commas. Example: -1000, 200, 300, 400, 500
- Finance Rate: The cost of capital or interest rate paid on borrowed funds.
- Reinvestment Rate: The rate at which positive cash flows can be reinvested.
The calculator returns the MIRR as a percentage. A project is generally considered acceptable if the MIRR exceeds the cost of capital.
Example Calculation
Consider a project with an initial investment of $10,000 followed by four years of cash inflows: $3,000, $4,000, $3,500, and $3,000. The finance rate is 8% and the reinvestment rate is 6%.
Enter: -10000, 3000, 4000, 3500, 3000 with a finance rate of 8% and reinvestment rate of 6%. The calculator returns an MIRR of approximately 9.2%. This means the project's return, adjusted for realistic reinvestment assumptions, is 9.2%.
Understanding Your MIRR Result
The MIRR represents the annualized return of the investment under the specified financing and reinvestment assumptions. A higher MIRR indicates a more attractive investment. Compare the result against your company's cost of capital or hurdle rate to make investment decisions.
Note that MIRR is sensitive to the rates you choose. Using a higher reinvestment rate will increase the MIRR, while a higher finance rate will decrease it. Always use rates that reflect realistic market conditions for your specific situation.
Common Mistakes When Using MIRR
- Using the same rate for finance and reinvestment: This defeats the purpose of MIRR. The advantage of MIRR is using different, realistic rates for each.
- Forgetting the negative sign on the initial investment: The first cash flow must be negative to represent an outflow. Omitting the negative sign produces an incorrect result.
- Confusing MIRR with IRR: MIRR will almost always be lower than IRR because it uses a more conservative reinvestment assumption. This is normal and expected.
- Ignoring the project timeline: MIRR assumes equal periods between cash flows. If your cash flows occur at irregular intervals, the result may not be accurate.
Limitations of MIRR
While MIRR improves upon IRR, it still has constraints. The calculation assumes that all positive cash flows can be reinvested at the specified reinvestment rate for the entire project duration, which may not hold true in practice. MIRR also does not account for project scale or duration differences when comparing multiple investments. For comprehensive analysis, pair MIRR with net present value (NPV) and payback period calculations.
Practical Use Cases for MIRR
- Capital budgeting: Evaluate long-term projects where reinvestment assumptions significantly impact projected returns.
- Comparing projects with different cash flow patterns: MIRR provides a more consistent ranking than IRR when projects have unconventional cash flows.
- Real estate investment analysis: Account for realistic reinvestment of rental income and property sale proceeds.
- Portfolio performance measurement: Adjust for the actual reinvestment rates available in the market.
Frequently Asked Questions
What is the difference between IRR and MIRR?
IRR assumes all cash flows are reinvested at the project's own IRR, which can be unrealistically high. MIRR lets you specify separate finance and reinvestment rates, producing a more conservative and realistic return measure. MIRR also avoids the multiple IRR problem that can occur with unconventional cash flow patterns.
Can MIRR be negative?
Yes. If the compounded future value of positive cash flows is less than the present value of costs, the MIRR will be negative. This indicates the project fails to return the cost of capital and should typically be rejected.
What finance rate should I use?
Use your company's weighted average cost of capital (WACC) or the interest rate you would pay to borrow funds for the project. For individual investors, this might be the rate on a margin loan or the opportunity cost of using cash reserves.
What reinvestment rate should I use?
Use a rate that reflects realistic reinvestment opportunities available to you. Common choices include the company's cost of capital, the return on similar-risk investments, or a conservative market rate like Treasury yields.
Is a higher MIRR always better?
Generally yes, but only when comparing projects of similar scale, duration, and risk. A project with a higher MIRR may still be less attractive if it requires significantly more capital or carries higher risk. Always consider MIRR alongside other metrics like NPV and payback period.