MIRR Calculator - Modified Internal Rate of Return

What does this MIRR calculator estimate?

Modified internal rate of return, or MIRR, estimates a project's annualized return while separating two assumptions that ordinary IRR blends together. It applies a financing rate to negative cash flows and a reinvestment rate to positive cash flows. That distinction can produce a more realistic comparison when a project requires later funding or when interim proceeds are unlikely to be reinvested at the project's own IRR.

The calculator starts with an initial investment at time zero and then evaluates a sequence of annual cash flows. It compounds every positive cash flow forward to the final year, discounts every negative annual cash flow back to time zero, and finds the single annual rate that connects those two totals across the project horizon.

How should each input be used?

Financing rate

The financing rate is the annual cost associated with funding negative cash flows. Use a percentage consistent with the project's borrowing cost, hurdle rate for committed capital, or another defensible funding assumption. The field is required for a complete MIRR calculation, accepts zero, and is applied only to negative cash flows after the initial investment. A higher financing rate reduces the present-value burden of later negative cash flows because those outflows are discounted more heavily; this can raise MIRR. A common mistake is entering a decimal such as 0.10 when 10% is intended. This calculator accepts either formatted percentages or plain numbers and interprets 10 as 10%.

Reinvestment rate

The reinvestment rate is the annual return expected on positive cash flows received before the project ends. Use a rate that reflects a realistic destination for interim proceeds, such as a treasury rate, portfolio return assumption, or corporate reinvestment opportunity. A higher reinvestment rate increases the terminal value of earlier inflows and therefore generally increases MIRR. Zero is valid and means positive cash flows do not grow after receipt. Do not automatically use the project's IRR; MIRR is designed precisely to avoid that often unrealistic reinvestment assumption.

Initial investment

Enter the time-zero project outlay as a positive dollar amount. The model automatically treats it as a negative cash flow. It is required for the usual investment interpretation, though a zero value is permitted for testing. A larger initial investment increases the present value of outflows and lowers MIRR when other inputs stay constant. Do not type the initial amount as negative, because that would reverse the intended meaning; the calculator validates the field and asks for a non-negative amount.

Annual cash flows

Each row represents the net cash flow at the end of that year. Positive numbers are inflows and negative numbers are additional investments, operating losses, or other outflows. Zero is allowed. Use “Add cash flow” to extend the horizon and the remove button to delete a period. The final remaining row determines the project horizon, so removing or adding years changes the exponent in the MIRR formula even when the new cash flow is zero. Enter net amounts rather than mixing revenues and costs unless those components have already been combined consistently.

How is MIRR calculated?

Let n be the number of annual periods. The model calculates the future value of positive cash flows at the end of year n and the present value of all negative cash flows at time zero. It then annualizes the ratio:

A positive inflow in year i is multiplied by (1 + reinvestment rate)ⁿ⁻ⁱ. A negative outflow in year i is divided by (1 + financing rate)ⁱ. The initial investment is already at time zero, so it needs no discounting. This framework is consistent with the logic used by spreadsheet MIRR functions; Microsoft's MIRR function documentation provides a useful cross-check for spreadsheet users.

How should the results be interpreted?

Modified internal rate of return

The primary result is the annualized rate connecting financed outflows with reinvested inflows. A positive MIRR means the terminal value of positive cash flows exceeds the present value of outflows over the stated horizon. A zero MIRR means the two totals are equal on an annualized basis. A negative MIRR means the terminal value is lower. MIRR is not a recommendation by itself; compare it with a consistent hurdle rate and with alternatives that have similar risk, timing, and scale.

Future value of inflows

This total shows what all positive annual cash flows are worth at the end of the project after compounding at the reinvestment rate. It rises with larger or earlier positive cash flows and with a higher reinvestment rate. A zero value means there are no positive inflows, so MIRR cannot be calculated.

Present value of outflows

This total includes the initial investment plus discounted later negative cash flows. It rises with a larger initial outlay or larger losses. A zero value means there is no investment base, so the MIRR ratio is undefined. The schedule makes each contribution transparent.

Nominal net cash flow and project horizon

Nominal net cash flow is the simple sum of all inflows minus the initial investment and later outflows; it ignores time value. It can differ materially from MIRR because timing matters. Project horizon is the number of annual rows and controls the annualization period.

How do the chart and schedule help?

The bar chart reveals the timing and sign of each cash flow. Early positive bars receive more years of reinvestment, while later negative bars are discounted over more years. The legend and summary table use the same current-state values as the plotted bars. The schedule then shows the exact factor and contribution used for every period, letting you reconcile the displayed future value and present value totals.

What are the main benefits and limitations?

MIRR avoids the multiple-solution problem that can affect ordinary IRR when cash-flow signs change more than once. It also replaces IRR's implicit reinvestment assumption with an explicit rate. However, the result remains sensitive to estimated cash flows and rates, and it compresses a complete project into one percentage. Review NPV, payback, risk, liquidity, and scenario ranges alongside MIRR. The World Bank's discussion of NPV, IRR, and modified IRR explains why metric selection depends on the decision context. For broader time-value intuition, the U.S. Securities and Exchange Commission's compound interest calculator illustrates how rates and time interact.

Common mistakes include mixing monthly and annual figures, omitting a terminal cash flow, double-counting the initial investment, using gross revenue instead of net cash flow, and comparing MIRRs built from inconsistent financing assumptions. Use scenario testing rather than relying on one forecast, and document the source of each assumption.