The Impact IRR formula integrates seven key elements into a single calculation of an impact investment's combined financial and impact performance. The formula is: ``` INPV = Σ [(Cₜ + Iₜ·(C₀/D)) / (1+r)ᵗ] − C₀, for t=1 to T ``` Where: - *T = Total number of periods - t = Measurement of time period(s) (e.g., year, month) - Iₜ = Projected impact return for the investment in period t - Cₜ = Projected financial return for the investment in period t - r = Cost of capital / hurdle rate - C₀ = Total initial investment - D* = Total investment with similar terms in the capital stack (e.g., equity, debt) The Impact IRR is determined by finding the rate r that makes the Impact NPV equal to zero.