Finally, one technical note is in order. The Mendoza example is simplified in the sense that it reflects a single cash out flow (time period 0) followed by a series of cash inflows. It is possible, however , that a project requires a series of cash outflows, beyond time period 0. To calculate the payback period in this case you should first sum these cash outflows to obtain an aggregate cash outflow for the project. To calculate the payback period you add the unadjusted cash out flows; for the discounted payback period, you would add together the present value of those cash outflows.