But how does he define "middle-income"? The Republican presidential nominee defined it Friday as income of $200,000 to $250,000 a year and less.
The definition of "middle income" or the "middle class" is politically charged as Romney and President Barack Obama fight to win over working-class voters. Romney would be among the wealthiest presidents, if elected, and Democrats have repeatedly painted him as out of touch with average people.
Obama also has set his definition for "middle class" as families with income of up to $250,000 a year.
Romney's comments came an interview broadcast Friday on ABC's "Good Morning America."
"No one can say my plan is going to raise taxes on middle-income people, because principle number one is (to) keep the burden down on middle-income taxpayers," Romney told host George Stephanopoulos.
"Is $100,000 middle income?" Stephanopoulos asked.
"No, middle income is $200,000 to $250,000 and less," Romney responded.
His campaign later clarified that Romney was referencing household income, not individual income.
The Census Bureau reported this week that the median household income -- the midpoint for the nation -- is just over $50,000.
Obama wants to extend Bush-era tax cuts for those making less than $250,000, while Romney wants to extend the tax cuts for everyone.
Romney has not explained how he would keep his plan from growing the nation's deficit.