It was a promise repeated many times by President Joseph R. Biden Jr.’s administration: The Internal Revenue Service would conduct more audits of wealthy Americans, but audit rates would not rise for households earning less than $400,000 per year.

Mr. Biden and the Democrats made that pledge as they bolstered funding for the I.R.S., hoping that more enforcement aimed at wealthy tax evaders would generate revenue to pay for climate and health care programs.

Republican lawmakers warned that more money for the I.R.S. would lead to more audits across the board, and that middle-class taxpayers would be targeted.

But new data released by the I.R.S. last week suggests that the agency upheld Mr. Biden’s promise in 2024. With an audit rate of 0.8 percent, people making over $500,000 on their latest return were more than twice as likely to be audited compared with the same point in the audit cycle in previous years.

Meanwhile, the matching audit rate for taxpayers making under $500,000 declined slightly. The figures covered 2022 tax returns that were filed in 2023 and audited during the 2024 fiscal year, which ended Sept. 30.