Together, the Big Five make up what percentage of the $3.8 trillion 2012 federal budget?

82%

Explanation:

The big five such as Defense, Medicaid, and Interest on Debt, Social Security, and Medicare are the five largest parts of the federal budget. The costs of these five federal budget areas can increase from time to time, but the increased would not be equally seen as expected by analysts.

Beyond 2012, the spending on defense and nondefense discretionary areas recorded slight increase as from 2016 while healthcare programs and Social Security were expected to double.