Deeper into debt.

Last month, the U.S. Senate voted to raise the national debt limit to nearly $9 trillion. (National debt is how much the federal government owes for money it has borrowed.) To write 9 trillion in digits, put down a 9, then add 12 zeros.

Mind-boggling? Consider the example that John Nolan gave the Reuters news agency to illustrate just one trillion. Nolan, a math professor at American University in Washington, D.C., said that you could reach that amount "if you spent a million dollars a day for a million days." The share for every man, woman, and child in the U.S. today is $30,000.

How did we run up so much debt? The U.S. has been spending far more than it takes in. To keep going, the government can earn more (raise taxes), spend less (cut services), borrow money, or do some combination of the three.

Given tax cuts and the high cost of the war in Iraq, the U.S. has had to raise its debt limit four times in as many years. To see how the debt has risen over the past half-century, see our graph at left.

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