1. Institutions shall calculate the own funds requirements for default risk using an internal default risk model for the portfolio of all trading book positions as referred to in Article 325bl as follows:
(a) the own funds requirements shall be equal to a value-at-risk number measuring potential losses in the market value of the portfolio caused by the default of issuers related to those positions at the 99,9 % confidence interval over a one-year time horizon;
(b) the potential loss referred to in point (a) means a direct or indirect loss in the market value of a position which was caused by the default of the issuers and which is incremental to any losses already taken into account in the current valuation of the position; the default of the issuers of equity positions shall be represented by the value for the issuers' equity prices being set to zero;
(c) institutions shall determine default correlations between different issuers on the basis of a conceptually sound methodology, using objective historical data on market credit spreads or equity prices that cover at least a 10 year period that includes the stress period identified by the institution in accordance with Article 325bc(2); the calculation of default correlations between different issuers shall be calibrated to a one-year time horizon;
(d) the internal default risk model shall be based on a one-year constant position assumption.
2. Institutions shall calculate the own funds requirement for default risk using an internal default risk model as referred to in paragraph 1 on at least a weekly basis.
3. By way of derogation from points (a) and (c) of paragraph 1, an institution may replace the one-year time horizon with a time horizon of sixty days for the purpose of calculating the default risk of some or all of the equity positions, where appropriate. In such case, the calculation of default correlations between equity prices and default probabilities shall be consistent with a time horizon of sixty days and the calculation of default correlations between equity prices and bond prices shall be consistent with a one-year time horizon.