Billionaire hedge fund manager Bill Ackman publicly broke with Donald Trump with a warning that the president's proposal to impose a one-year, 10 percent cap on credit card interest rates would backfire by cutting off credit to millions of Americans.

In a now-deleted post on X, Ackman said the proposed cap would make it impossible for lenders to price risk adequately, forcing credit card companies to cancel cards for large numbers of consumers, particularly those with weaker credit, pushing them toward far costlier and riskier alternatives.

'This is a mistake president,' Ackman wrote on Friday. 

'Without being able to charge rates adequate enough to cover losses and to earn an adequate return on equity, credit card lenders will cancel cards for millions of consumers who will have to turn to loan sharks for credit at rates higher than and on terms inferior to what they previously paid.'

Ackman's comments came hours after Trump announced on Truth Social that his administration would seek to cap credit card interest rates at 10 percent for one year beginning January 20, 2026. 

Trump framed the move as part of a broader effort to address affordability and rein in lenders charging rates of '20 to 30%.'

Ackman's criticism came only hours after Trump unveiled the idea on Truth Social, framing it as a populist strike against what he described as abusive lending practices in an economy still grappling with high household debt.

'Please be informed that we will no longer let the American Public be 'ripped off,' Trump wrote. 

Billionaire hedge fund boss Bill Ackman publicly blasted President Donald Trump's proposed 10% credit card interest cap as a 'mistake'

'This is a mistake President,' Ackman wrote in a blunt X post that was later deleted

In a follow-up tweet, Ackman said Trump's goal of lowering rates was 'worthy and important,' but the 10% cap would inevitably shrink access to credit

'Effective January 20, 2026, I, as President of the United States, am calling for a one year cap on Credit Card Interest Rates of 10%.'

Trump said the move was aimed squarely at lenders charging interest rates in the '20 to 30%' range - a figure common for many credit cards, particularly for borrowers with weaker credit profiles. 

Any nationwide cap on interest rates would almost certainly require congressional approval, and it remains unclear what legal pathway the White House could use to impose such a restriction.

By Saturday morning, Ackman, the CEO of Pershing Square Capital Management, had reposted his argument in a longer statement, softening his tone toward Trump personally while doubling down on the substance of his warning.