The figure is also miniscule compared to the many hundreds of billions the government earns from the alternative minimum tax, which Obama's budget last month said he would replace with the Buffett rule tax.
The alternative minimum tax, originally aimed at ensuring that wealthy Americans pay taxes despite deductions and other breaks, has begun affecting upper middle-class families, and Congress acts every year to minimize its impact.
In an analysis provided to The AP on Tuesday, Congress' Joint Committee on Taxation estimated that a bill introduced last month by Sen. Sheldon Whitehouse, D-R.I., enshrining Obama's proposal into law would collect $31 billion over the coming 11 years.
Obama has proposed requiring that people earning at least $1 million annually pay at least 30 percent of their income in taxes. The plan is named for billionaire investor Warren Buffett, who has said that taxes on the wealthy are not high enough.
The proposal has become a leading symbol of Obama's and congressional Democrats' election-year efforts to persuade voters that they are the party championing economic fairness.
Republicans have mocked the plan as one aimed at scoring political points that would have little real budgetary impact. "Now that we have this analysis, I hope the president will stop the class warfare and start leading by putting out real proposals to bring down our debt, get rid of the AMT and reform our broken tax code," Sen. Orrin Hatch of Utah, top Republican on the Senate Finance Committee, said in a written statement, using the alternative minimum tax's acronym.
Hatch's Finance committee GOP aides requested the study.
Whitehouse said that other groups, including the respected bipartisan Tax Policy Center, have estimated that the proposal could earn more than $31 billion. "No matter how you slice it, that's real money that could help bring down our deficit. Most important: It's simply the right thing to do," he said in a statement.
Whitehouse's bill would require people making at least $2 million a year pay at least 30 percent of their earnings in taxes, though they could deduct certain amounts for their charitable contributions. The tax would be phased in for people earning at least $1 million annually.
Obama has not spelled out details of how his proposal would work.