Load peak forecasting (LPF) is an important decision tool in a deregulated market in order to help the operator to choose the best efficient mix production for the next day, satisfying the demand. The construction of the first built price of energy (€/MWh) is made until 11 p.m. of the day before. For example, in the case of MIBEL (Iberian Electricity Market), there is one starting session during the day before and seven-intra sessions during the current day. The concept of the Dynamic Tariffs (DT) is bringing to the low voltage consumer a certain 'dynamic' in the energy prices, (which are indexed to the MIBEL prices), during several hours of the day instead of a traditional fixed price of energy. For peak load time the price increases and for the empty hours the price is cheaper. The result of these actions is to shift peak load consumption to the low-peak periods. In this paper, the results of the forecasts were evaluated, simulating their effects in the environment of DT and comparing them with actions that would be taken knowing in advance the real diagram of the consumption. This paper presents a methodology for 24 hours forecasting loads and it was incorporated in a dynamic tariff environment. The model was applied to a case study. The active power data was collected in EDP Distribution System in the city of Lisbon.