A plan by global regulators to lift a key backstop capital measure all depends on how you add it up.

The Basel Committee on Banking Supervision, in a plan scheduled to be released on April 6, is weighing how to raise a bank's leverage ratio, which measures capital against total assets, from the current threshold of 3%. At the same time, the regulatory body is considering how banks account for risky assets, particularly derivatives, complex instruments that try to deliver double or even triple returns of the indexes they track.