If you are evaluating several competing investments with different life cycles, then you should also include a calculation known as Equivalent Annual Annuity (EAA). Unlike NPV (Net Present Value) which does not take into consideration the life cycle of the investment, EAA factors the life cycle into the calculation so that you have a better basis for comparing different investments that have unequal lives. EAA uses the annuity payment formula. In Microsoft Excel, this is =PMT with three parameters: Hurdle Rate, Length of Investment, and NPV with a minus sign in front.
For example, suppose we have two investments, A and B. Investment A has a 6 year life and investment B has a 8 year life. The Hurdle Rate for discounting the cash flows is 10%. After Tax Cash Flows are listed into the spreadsheet per the illustration below: