[ See also Net Present Value @ Wikipedia ]

NPV = \sum_{i=0}^n \frac{R_{ti}}{(1+r)^t_i} = R_0 + \sum_{i=1}^N \frac{R_{ti}}{(1+r)^{t_i}}

where

 – time passed since the first investment ( assuming that ),

 – the discount rate, i.e. the return that could be earned per unit of time on an investment with similar risk

 – total number of time steps

 – the net cash flow at time step t. 

 – the volume of cash investment at initial time moment .