Semi-variable expenses cannot be used for budgeting, cost analysis and cost control in their composite form. For these purposes, they have to be broken down into their fixed and variable components. Some of them, as factory supervision for instance, can be analyzed without difficulties from payroll records or from experience, while others are more or less resistant to the ordinary analytical approach. The practice of estimating the size of the fixed and variable parts can yield only approximations and is open to considerable errors. The best and easiest approach is the algebraic method of segregation. It yields much more accurate results than estimating without being more difficult in its application. Heretofore, the method has been used mainly for overall analyses of annual or monthly cost and budget figures with the aid of a formula which discloses the aggregate of the variable components of a given sales cost relationship. The formula is excellent and can, with two supplementary formulas, be applied for the segregation of the fixed and variable parts in every semi-variable expense category.