Income Tax Act of 1916
The United States Revenue Act of 1916, (ch. 463, 39 Stat. 756, September 8, 1916) raised the lowest income tax rate from 1% to 2% and raised the top rate to 15% on taxpayers with incomes above $2 million. (Previously, the top rate had been 7% on income above $500,000.) The Act also instituted the federal estate tax.
The entry of the United States into World War I greatly increased the need for revenue.
An excess profits tax was introduced and the modern estate tax was imposed.
The act was applicable to incomes for 1916.
A Normal Tax and an Additional Tax were levied against the net income of individuals as shown in the following table.
Corrected for inflation by CPI:
...
Wikipedia