In the article the author's approach to improving the methodology of provision for possible loan losses on corporate lending assets. Author developed a model assessing the quality of credit assets with a view to the formation of reserves, market-based approach. The methodical approach to the calculation of the amount of credit impairment of assets and determination of the allowance for credit operations. The model can be used by banks, investment funds in the formation of financial reporting and analysts to assess the risks, reserves, economic capital in accordance with modern standards of banking supervision.