$$$ = $$$

Even if we could balance the federal budget going forward (i.e., revenue = spending), our national debt would continue to automatically rise due to the interest on that debt. Currently, interest on the U.S. national debt is the third largest component of government spending, following national defense spending.  Why so high?  Well, consider the amount of interest associated with a $17.5 trillion debt, which is rising automatically as well.

Conclusion:
To balance the budget, revenue must equal spending + additional interest on the expanding debt.