In the United States, depository institutions are subject to risk-based capital guidelines issued by the Board of Governors of the Federal Reserve System (FRB).[4] These guidelines are used to evaluate capital adequacy based primarily on the perceived credit risk associated with balance sheet assets, as well as certain off-balance sheet exposures such as unfunded loan commitments, letters of credit, and derivatives and foreign exchange contracts. The risk-based capital guidelines are supplemented by a leverage ratio requirement. To be adequately capitalized under federal bank regulatory agency definitions, a bank holding company must have a Tier 1 capital ratio of at least 4%, a combined Tier 1 and Tier 2 capital ratio of at least 8%, and a leverage ratio of at least 4%, and not be subject to a directive, order, or written agreement to meet and maintain specific capital levels.