Apple's actual U.S. tax bill is far lower than the company tells investors, according to a Senate panel report.

The Cupertino, Calif. company under fire now for its tax strategy, paid $8.4 billion less in U.S. taxes over a three-year period than the company told investors, according to the report released earlier this week ahead of CEO Tim Cook's testimony before the Senate.

All public companies estimate their tax bill in earnings reports and overestimates are common. However, what's unusual in Apple's case is that the difference between the company's stated tax bill and the amount it actually paid grew between 2009 and 2011.

“The differences widened substantially over the three-year period, expanding from a 2009 difference of $1.4 billion to a 2011 difference of $4.4 billion,” the report said.

As the report notes, there are legitimate reasons for the discrepancy; companies tell shareholders the amount they’ve set aside to pay U.S. taxes, but often that money doesn’t end up with the IRS immediately or ever. That’s because companies are required to report to investors and the SEC how much they think their taxes will lower their profits, but are often able to reduce that liability through a variety of legal creative accounting strategies.

For example, a company may tell investors how much money it would owe in taxes on profits housed overseas if the company brought that cash back to the U.S. But often, as in Apple’s case, the company has no plans to bring that money back home.

Apple didn't immediately respond to an e-mail message seeking comment.

"It's very dangerous to use a company's stated tax expense to make statements about what it actually pays in taxes," Douglas Shackelford, a University of North Carolina expert on taxes and accounting told Fortune in a report last year.

The finding was one of many in the Senate report that focused largely on the Irish subsidiaries Apple uses allegedly to avoid paying taxes on billions in profits to any government.

Apple’s CEO Tim Cook told the Senate panel in a hearing Tuesday that the company pays “all the taxes we owe.” Apple paid $6 billion in U.S. taxes for the fiscal year ended in September, according to the Wall Street Journal and Cook claimed in the Senate hearing that the company is the “largest corporate taxpayer in America.”

(Hat tip: The Wall Street Journal)

Also on HuffPost:

Loading Slideshow...
  • 10. General Electric

    <strong>Increase in profits held offshore in 2012:</strong> + $6 billion <strong>Total offshore profit holdings as of 2012:</strong> $108 billion <strong>Headquarters:</strong> Connecticut In an email to The Huffington Post, GE wrote that "more than half of our business is outside the U.S., and we need to be able to fund that business using overseas profits. Most of our earnings invested outside the U.S. are in active business operations like manufacturing facilities, and loans to non-U.S. customers."

  • 9. IBM

    <strong>Increase in profits held offshore in 2012:</strong> + $6.5 billion <strong>Total offshore profit holdings as of 2012:</strong> $44 billion <strong>Headquarters:</strong> New York IBM did not respond to HuffPost's requests for comment via email and phone.

  • 8. Citigroup

    <strong>Increase in profits held offshore in 2012:</strong> + $6.7 billion <strong>Total offshore profit holdings as of 2012:</strong> $42.6 billion <strong>Headquarters:</strong> New York A phone call to Citigroup requesting comment was not returned.

  • 7. Johnson & Johnson

    <strong>Increase in profits held offshore in 2012:</strong> + $7.4 billion <strong>Total offshore profit holdings as of 2012:</strong> $49 billion <strong>Headquarters:</strong> New Jersey Johnson & Johnson declined to comment.

  • 6. Abbott Laboratories

    <strong>Increase in profits held offshore in 2012:</strong> + $8 billion <strong>Total offshore profit holdings as of 2012:</strong> $40 billion <strong>Headquarters:</strong> Illinois Abbot Industries did not respond to HuffPost's request for comment.

  • 5. Google

    <strong>Increase in profits held offshore in 2012:</strong> + $33 billion <strong>Total offshore profit holdings as of 2012:</strong> $8.5 billion <strong>Headquarters:</strong> California Google declined to comment to HuffPost.

  • 4. Merck

    <strong>Increase in profits held offshore in 2012:</strong> + $9 billion <strong>Total offshore profit holdings as of 2012:</strong> $53.4 billion <strong>Headquarters:</strong> New Jersey “Merck files its income tax returns in accordance with all applicable laws and regulations," the company wrote in an email to HuffPost.

  • 3. Pfizer

    <strong>Increase in profits held offshore in 2012:</strong> + $10 billion <strong>Total offshore profit holdings as of 2012:</strong> $73 billion <strong>Headquarters:</strong> New York Pfizer did not return HuffPost's request for comment.

  • 2. Microsoft

    <strong>Increase in profits held offshore in 2012:</strong> + $16 billion <strong>Total offshore profit holdings as of 2012:</strong> $60.8 billion <strong>Headquarters:</strong> Washington In response to the study, Microsoft referred to a 2012 Senate hearing testimony by the company's corporate vice president for worldwide tax, Bill Sample. "In conducting our business at home and abroad, we abide by U.S. and foreign tax laws as written," Sample said. "That is not to say that the rules cannot be improved -- to the contrary, we believe they can and should be."

  • 1. Apple

    <strong>Increase in profits held offshore in 2012:</strong> + $28 billion <strong>Total offshore profit holdings as of 2012:</strong> $82.6 billion <strong>Headquarters:</strong> California HuffPost's requests for comment via email and phone were not returned by Apple.