EVM is a project management technique for measuring project performance and progress in an objective manner. Regarding costs and even more exact the budget of the project RationalPlan helps project managers to have a clear overview.
Once established an initial estimative project budget it can be compared at any moment within the project evolution with the actual project cost. The so called Budget Variance will tell the project manager if it is over or under budget.
Budget Variance = Completion * Budget - Actual Cost
A budget variance greater than 0 is good. A negative value means that the initial budget estimate was an underestimate value.