WITH indexing - the income levels to which the tax rates applied must be adjusted for inflation. The tax structure was sufficiently graduated (not "progressive" - there is no progress in it) in 1913.
Here are the original values:
Marginal Tax Brackets Tax Rate Over But Not Over
1.0% $0 $20,000 2.0% $20,000 $50,000 3.0% $50,000 $75,000 4.0% $75,000 $100,000 5.0% $100,000 $250,000 6.0% $250,000 $500,000 7.0% $500,000 -And here are those values adjusted for inflation:
Marginal Tax Brackets Tax Rate Over But Not Over
1.0% $0 $453,292 2.0% $453,292 $1,133,230 3.0% $1,133,230 $1,699,846 4.0% $1,699,846 $2,266,461 5.0% $2,266,461 $5,666,152 6.0% $5,666,152 $11,332,304 7.0% $11,332,304 -This is about right. No one can complain about this. There is no reason that the rates should rise over time.