"The biggest part by far is the spending and the income created by you and me -- and all the other consumers in the country. In fact, consumer spending accounts for three-quarters of that $12 trillion," says Dr. Walden, a North Carolina Cooperative Extension specialist.

"Secondly we have the spending done by businesses -- particularly in terms of their investments in new structures, equipment and technology
So that's an important component," he adds.

"Then we can't forget government. Government does play a role here simply because it's so large. And we have a lot of government spending as mundane as picking up the garbage to building roads and bridges and funding the military at the national level," he says.

"And then the fourth component is international trade. And the way this works here is that exports from our country sold in other countries -- that's a plus -– that adds to our national income.

"But imports –- things we are buying from other countries -- that's a negative, and so that brings down that $12 trillion."