Modified Internal Rate of Return or MIRR is the discount rate that equates the present value of investments (outflows) with the future value of incoming cash flows (inflows):
\begin{align} \sum_{i=0}^{t}\frac {COF_{i}}{(1+r)^{i}} &=\frac {\sum_{i=0}^{t}CIF_{i}(1+r)^{t-i}}{(1+MIRR)^{t}} \\ PV_{COF} &=\frac {FV_{CIF}}{(1+MIRR)^{t}} \\ MIRR &= \sqrt[t]{\frac{FV_{CIF}}{PV_{COF}}}-1 \end{align}
t— number of periods;
r— discount rate (e.g., weighted average cost of capital);
COF— cash outflow;
CIF— cash inflow.