Mitt Romney is acknowledging that it's impossible to know how his tax plan will affect the federal budget deficit.
In an interview Wednesday on CNBC, the former Massachusetts governor scoffed at outside groups who have said his plan to lower marginal tax rates would increase the deficit.
Romney said he was surprised that such assertions were being made because his plan "can't be scored." He says he'll have to work with Congress on the details before he can estimate how much the plan will cost.
Romney previously has insisted that his plan to cut marginal individual tax rates by 20 percent won't increase the deficit because he would limit deductions and exemptions for the wealthy. He hasn't outlined what those changes would be, and says he'll work with Congress.