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.