The ratio acts as a backstop to a lender's core risk-weighted capital requirements. A ratio of 3 percent means a bank must hold capital equivalent to 3 percent of its total assets.
The rule is part of the Basel III accord endorsed by world leaders in response to the 2007-09 financial crisis that left taxpayers rescuing undercapitalized lenders.
The rules have been drafted by the Basel Committee and on Sunday its oversight body, the Group of Governors and Heads of Supervision (GHOS), chaired by European Central Bank President Mario Draghi, backed key changes to the leverage ratio.
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"The final calibration, and any further adjustments to the definition, will be completed by 2017," the GHOS said in a statement after its meeting in Basel, Switzerland.
As first reported by Reuters last month, when banks tot up their assets, they can now include derivatives on a net rather than the much bigger gross basis so they don't have an incentive to ditch some types of assets, such as loans to companies, to avoid hitting the ratio's ceiling.
U.S. banks will welcome the change because their accounting rules have allowed them to net derivatives, while European banks, whose accounting rules require gross positions, will be able to net and not be at a disadvantage to U.S. rivals.
The GHOS has endorsed new criteria which all banks must meet if they are to net derivatives and repurchase agreements for leverage ratio calculations, irrespective of what accounting standards they follow.
This will also make it easier for investors to compare banks. Banks must start disclosing their leverage ratio from 2015, and comply with the Basel minimum ratio from January 2018.
"The revised approach to same-counterparty short-term financing transactions recognizes the benefit of netting in reducing systemic risk and is welcome, as is the lower conversion factor for trade finance transactions which banks provide to oil the wheels of international trade and economic growth," said Simon Hills, a director at the British Bankers' Association.
U.S. and UK regulators have come to favor the leverage ratio as a main tool for checking on bank risks rather than just a backstop, as they suspect lenders are gaming the risk weighting system used to determine core capital buffers.
U.S. banks are being asked to have leverage ratios well above 3 percent and some lawmakers in Britain want a ratio of 4 percent or more.