It said that the delay was because of the amount of work it will take after uncovering a number of "material weaknesses" in its internal control.
Interpublic, owner of agencies including McCann Erickson and Initiative, also said that it might have to make adjustments to previous financial statements. These mainly concern acquisitions made from 1996 to 2001, and could add up to $145m (£75m) in revenues.
If this happens, it will be the second time in just over two years that Interpublic has been forced to restate its results. In November 2002, it revealed that it overstated revenues by $180m over a four-year period.
In a statement today, Interpublic said that it would not be able to file by March 31, which is the latest due date according to US financial regulations.
Michael Roth, who took on the chairman and chief executive role in January this year, said: "The extensive review process we have undertaken is appropriate given the material control weaknesses we face.
"We were unable to provide details concerning the status or timing of our filing and earnings release until having come to this point in our process. We regret this, as well as the delay that will result."
However, he sought to assure clients that it was business as usual, saying: "These actions are not related to and should not impede the professional performance of our operating units, many of which continue to make great strides and deliver outstanding work and results to their clients."
While Interpublic seeks to draw a line under its financial problems, it has put in a solid new-business performance of late, winning the $300m Intel account this week, and also taking the £100m pan-European Nokia N-series account in February.
However, investors were unhappy with the news and sent its share price tumbling by 14 cents to $12.21 this morning, a fall of 1.1%.
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