Per the AT Candidate Handbook:
Candidates may take any individual exam up to three times within a 365-day period. A 90-day waiting period is required prior to each retesting attempt. During the initial 365-day period candidates are eligible for a reduced retake fee of $300 USD. If a candidate does not pass the exam upon their third attempt, there will be a waiting period of 365 days from the date of the third attempt to reapply to take the exam. With each new application submission, candidates will be required to meet the eligibility requirements in effect at the time of submission and will need to reapply at the full price of $625 USD.
Retake Application