When creating a firm or when we intend to value an ongoing concern it is very important to have reliable and consistent financial statements in order to make the proper decisions not only for the starting of a new firm but for the following up and monitoring that firm or simply an ongoing concern. In this guide we show a very clear and simple step by step procedure to construct proforma financial statements. From these financial statements we will derive the cash flows necessary to calculate the market value and net present value (NPV) for the firm. We calculate the traditional break even points and what we call the dynamic break even points. We present some complexities and show a simple sensitivity analysis that includes the determination of critical variables and scenario analysis. Palabras clave: Proyeccion de estados financieros, valor presente neto, VPN, valoracion de empresas, valoracion de flujos de caja, costo de capital, analisis de punto de equilibrio, analisis de sensibilidad, escenarios