Although many final rules mandated by the Dodd-Frank Act are still not in place two years after its passage, Standard & Poor's has nevertheless taken a crack at estimating what those reforms will cost the nation's largest banks.

In a new report, "Two Years On, Reassessing the Cost of Dodd-Frank for the Largest U.S. Banks," Standard & Poor's Ratings Services has updated its previous estimate of what new regulations might cost Bank of America, Citigroup, Goldman Sachs, JPMorgan Chase, Morgan Stanley, PNC Financial Services, U.S. Bancorp, and Wells Fargo. It says these “large, complex” institutions “will bear the brunt of the financial impact.”

Standard & Poor's estimates that the Dodd-Frank Act could reduce pretax earnings for these eight banks by a total of $22 billion to $34 billion annually, an increase from the previous estimate of $19.5 billion to $26 billion. The full impact of the regulations could mean a drop in pretax return on equity of between 250 to 375 basis points for the biggest banks, it predicts.

"Considering what we know now about rules and regulations that have yet to be implemented, and based on our current forecasts for banks' capital and earnings, we don't believe the financial impact of regulatory reform will, in itself, affect our ratings on the eight large U.S. banks," said Standard & Poor's credit analyst Matthew Albrecht in a statement. "However, proposed rules and regulations could change our assessments of banks' business or risk positions, which could ultimately lead to rating actions in isolated cases."

He added that most of the higher estimate reflects a view that regulators “could take a more strict interpretation of the Volcker Rule” than was previously expected. That ban on proprietary trading by commercial banks could start having an affect on results toward the end of 2013 or beginning of 2014, the ratings agency says.