Theoretical model of macroprudential add-ons to risk-weights for foreign-currency denominated loans

We offer a Merton-Vasicek model extension to account for the presence of foreign-currency denominated loans in the portfolio and to derive the value of the macroprudential add-ons to risk-weights in the capital adequacy ratio. We show how the add-ons depend upon the foreign-currency exchange rate volatility, and upon the ratio of foreign-currency denominated assets and liabilities of typical borrowers within such a loan portfolio. In addition, we explain why it is worth accounting for the exchange rate in the additive, and not multiplicative form in the theoretical model.