When did the federal income tax become a permanent institution in the U.S.?

The federal income tax in the U.S. has been permanent since 1913, with the passage of the 16th Amendment.

As established in that year, the bottom rate was 1 percent on taxable net income over $3,000 for an individual, $4,000 for a married couple.

The top rate, for those making more than $500,000, was 7 percent.