Corporate profits are cyclical, running up during booms and down during busts. The recent recovery in corporate profits has been influenced by Fed expansionary monetary policy.
http://research.stlouisfed.org/fred2/series/CP?cid=109
National income varies much less. So as a percent of national income, profit vary quite a bit.
http://research.stlouisfed.org/fred2/series/NICUR?cid=109
As the charts show, in Q3 2012, national income was $13,912 billion and corp. profits were $1,752 billion. So corp. profits were 12.6% of national income.
