The USMLE program is introducing a limit on the total number of times an examinee can take the same Step or Step Component. When this limit takes effect, an examinee will be ineligible to take a Step or Step Component if the examinee has made six or more prior attempts to pass that Step or Step Component, including incomplete attempts.

The effective date for the six-attempt limit depends upon whether an examinee has taken any Step or Step Component (including incomplete attempts) before January 1, 2012.

Examinees Who Have NOT Taken Any Step Or Step Component Before January 1, 2012
If you have not taken any Step or Step Component before January 1, 2012, the six-attempt limit will go into effect for all exam applications that you submit on or after January 1, 2012.

Example 1: On January 15, 2012, Examinee A submits his application for his first attempt at any Step or Step Component. The six-attempt limit will be effective at that time for all Steps and Step Components and Examinee A will be allowed to take each Step or Step Component no more than six times, including incomplete attempts.

Examinees Who Have Taken Any Step Or Step Component Before January 1, 2012
If you have taken any Step or Step Component (including incomplete attempts) before January 1, 2012, the six-attempt limit will go into effect for all exam applications that you submit on or after January 1, 2013. Beginning on that date, all attempts at a Step or Step Component will be counted toward the limit, regardless of when the exams were taken.

Example 2: Examinee Bs application for a seventh attempt at a particular Step or Step Component is received on December 15, 2012. For this examinee, the six-attempt limit will not prevent the seventh attempt, since the application was submitted before January 1, 2013. However, if Examinee B fails the exam, he will not be eligible to submit an application on or after January 1, 2013 to retake that Step or Step Component.

Example 3: Examinee C attempts to submit an application for a seventh attempt at a particular Step or Step Component on or after January 1, 2013. The application will not be processed, since all exam applications submitted on or after January 1, 2013 will be subject to the six-attempt limit.

Source: New Attempt Limit for USMLE Examinations ECFMG News