"You'd have to get rid of the vast majority of deductions and credits in the tax code to make it work, including some sacred cows like the mortgage interest deduction, child tax credit, etcetera," Kasprak said.
Spokeswoman Andrea Saul said Romney envisions changes to create a "fairer and simpler tax system," but did not give details.
Here's how the plans the two candidates have described so far would play out in 2013. The numbers are from calculations by Citizens for Tax Justice, corroborated by the Tax Foundation (although it would use slightly lower figures for Obama that exclude employer-paid Social Security and Medicare payroll taxes):
Assuming inflation-adjusted earnings of $23 million, he'd pay an effective rate of 34 percent under the Obama plan. That drops to 13 percent under Romney's own tax proposal — even lower than the 15 percent he estimated for 2011, which irritated critics who felt a multimillionaire investor should shoulder a higher rate than middle-class working families.
The difference between the two candidates' plans: paying the taxman $7.8 million vs. $3 million.
Like others who are taxed at earned income instead of investment rates, Obama's bill wouldn't swing as dramatically under the differing plans. He reported paying an effective tax rate of almost 21 percent on about $790,000 in income in 2011. Under his plan, that would climb to 28 percent. Under Romney's plan, it drops to 18 percent.
The difference: $248,000 vs. $158,000.
The figures were based on Obama's 2011 tax return and Romney's 2010 return. Romney has filed for an extension and released only preliminary 2011 numbers.
Bob McIntyre, director of Citizens for Tax Justice, said Romney's savings for the wealthy come at the expense of everyone else.
"If we have more tax cuts for the rich, or even keep the ones we have now, then somebody's got to pay for it," McIntyre said, either in higher taxes or by losing government services.
At the Tax Foundation, Kasprak called Romney's plan a step in the right direction because it would lower tax rates overall and thin the tangle of deductions and credits. He called Obama's proposal "complex and arbitrary."
Odds of either candidate getting his full plan through Congress after the Nov. 6 election are slim. Efforts to reform the tax code have been mired in partisan bickering for years. But pressure is building to do something.
"Just because Romney wins or Obama wins doesn't mean that what they're proposing becomes law," said Charney of H&R Block. "What may be more likely is bits and pieces happening."
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