Earned Value is a well-known project management tool that uses information on cost, schedule and work performance to establish the current status of the project. By means of a few simple rates, it allows the manager to extrapolate current trends to predict their likely final effect. The method is based on a simpli-fied model of a project, but proved to be useful in practice of cost control. It is being developed to account better for schedule and time aspects. The paper outlines the basic principles of the method and its recent extension, the Earned Schedule method, and, with help of a few examples, investigates into assumptions that affect their diagnostic and predictive accuracy.