Wessel, director of the Hutchins Center on Fiscal and Monetary Policy, explains:
Of course, all this money has to come from somewhere. This year, Washington will borrow about 14 cents for every dollar it spends. (That’s a sharp contrast to the worst year of the recession when it borrowed 44 cents for every dollar spent.) The rest comes from taxes. Measured as a share of the economy, taxes in the current fiscal year will be about 17.5% of GDP, roughly in line with the 17.4% average for the past 40 years. But the source of those revenues has changed significantly over the years: The payroll tax levied on wages to financial Social Security and Medicare accounts for a growing share of federal receipts; the tax on corporate profits represents a shrinking share.
This year, about 46% of all revenues come from the individual income tax, 34% from the Social Security/Medicare payroll tax and 12% from taxes on corporate profits. Forty years earlier, it was 45% from the individual income tax, not much change there. But 15% came from the Social Security/Medicare payroll tax and 29% from taxes on corporate profits.
Read the full post which includes additional charts about understanding the federal budget.