I want to use an excel spreadsheet to calculate the value of a flow of net income at a certain rate. Lets say the net income (revenues less expenses) is for 10 years. Ex; value of a commercial building with a purchase price, a stream of revenue and expenses over ten years discounted a certain rate

NPV() is a standard Excel Function.

Enter =NPV( into a cell, then click on the Insert Function icon (just to the left of the formula bar) and fill in the parameters.

Press F1 in Excel and read up directly on NPV as a function.