Indirect effects ("leakage") are an important issue in baseline development for CDM and JI projects but so far no coherent methodology for their determination has been suggested. We propose a simplified method to correct direct emission reduction values for leakage. A matrix of different project types should be elaborated that shows leakages in qualitative form. Depending on the number of entries in the matrix columns, an overall leakage factor will be calculated by summing up factors related to the cell entries. The factors have predetermined values denominated in per cent to cover the different qualitative degrees of leakage.