The fund used its annual healthcheck on the world's biggest economy to spell out the dangers of failure, which would likely include the US government defaulting on its debt for the first time in its history.
"It should be self-evident a debt default by the US government would have very serious, far-reaching and dramatic repercussions," said John Lipsky, the IMF's acting managing director. "That's why were are confident it will be avoided."
Republicans and Democrats have been locked in tense negotiations for the past month on how to raise the country's $14.3 trillion (£8.9 trillion) debt ceiling, which the Treasury has said will be reached on August 2.
The talks, which Republicans walked out of last week, are widely seen as a forerunner of the battle over the deficit that will be central to next year's presidential election.
President Barack Obama, who stepped into the talks this week, said that "we don't know how capital markets will react" should an agreement not be struck. Ratings agency S&P said yesterday that the US would have its AAA credit rating slashed if it missed an interest payment on its debts after the deadline. (read more)