An algorithm to simulate and estimate the savings in electricity consumption costs of micro, small and medium size enterprises (MSMEs) has been used, and its reliability has been verified in an enterprise. The methodology includes Peruvian regulations to determine the charges corresponding to each electrical tariff, and thus can be applied for any kind of MSME in low and medium voltage. From the electricity consumption profile and tariff in three representative MSMEs it was possible to simulate the changes in the electricity tariff and the rating factor. With this methodology it was possible to identify the most convenient tariff for each MSMEs considering their rating factor during peak hour (PH) and non-peak hour (NPH). The satisfactory results of the simulation show that the methodology represents an important tool to increase the productivity and competitiveness of these economic units.