USMLE & ECFMG Rules in General:

Retaking a USMLE Step:

• There is no limit on the number of attempts to pass each USMLE Step.
• There is a minimum wait period of 60 days between consecutive attempts and a limit of three attempts in a 12-month period.
• For USMLE Step 1 and Step 2 CK: You can retake the exam no earlier than the first day of the month that begins at least 60 days after your previous test date.
• For Step 2 CS and Step 3: Your eligibility period for the retake will begin no earlier than 60 days after the date of your prior attempt.
• For Step 3: You may not reapply sooner than 60 days after your last attempt.

USMLE General Rules that you should know:

• If you pass a Step or Step Component, you are not allowed to retake it.
• To be eligible to register for USMLE Step 3, you must have passed Step 1, Step 2 CK and Step 2 CS.
• You can take the Step 1, Step 2 CS or Step 2 CK in any order or sequence that you wish (provided you fulfill all eligibility requirements)
• Individuals who have passed Step 2 prior to the implementation of Step 2 CS are not permitted to take Step 2 CK.

USMLE Step 3 eligibility:

To be eligible to apply and register for USMLE Step 3, you must have

• Graduated from medical school and obtained a MD / DO degree (or its equivalent)
• Passed Step 1, Step 2 CK, and Step 2 CS 
• Should be ECFMG Certified.
• Fulfill other requirements as determined by the state medical licensing board to which you are applying (residency requirements etc).

Number of Attempts and Time Limits:

• There is no limit on the total number of times you can retake a USMLE Step or Step Component you have not passed.
• However, USMLE recommends to state medical licensing boards
• that the state medical boards have a time limit of 7 years within which you should have passed Step 1, Step 2, and Step 3 examinations.
• that the state medical boards allow no more than six attempts to pass each Step or Step Component
• The ultimate decision on accepting these above USMLE recommendations rests on the state medical licensing boards. This is the reason that there are so many confusing requirements from each state medical licensing authority.
• Visit residency Forum to discuss state specific medical licensing requirements. http://residencyandfellowship.com/ipw-web/bulletin/bb/ 
• Time limit for completion of all three Steps: The time period may start from the date the first Step or Step Component is passed (or in some states from the date of the first attempt – even if you didn’t pass that attempt)
• For state-specific medical licensing requirements, Visit the FSMBhttp://www.fsmb.org/