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How long are Security Clearances valid?
A Periodic Reinvestigation (PR) is required every 5 years for a TOP SECRET Clearance, 10 years for a SECRET Clearance, or 15 years for a CONFIDENTIAL Clearance. However, civilian and military personnel of DOD can be randomly reinvestigated before they are due for a PR.
When a security clearance is inactivated (ie, when someone gets out of the military, or quits from their government civilian job or contractor job), it can be reactivated within 24 months, as long as the last background investigation falls within the above time-frame.
For example, if a military person has a Top Secret Clearance, and gets out of the military, and applies to work for a civilian contractor, the military member's clearance can be reactivated within 24 months of getting out of the military, as long as his last Top Secret Background investigation is less than five years old.
A security clearance is a valuable commodity outside of the military. This is because civilian companies who do classified work for DOD must bear the cost of security clearances for their employees, and clearance investigations can cost several thousands of dollars. Because of this, many DOD contractors give hiring preference to ex-military personnel with current clearances. However, you want to do your job-hunting right away, after separation. Once your clearance expires, you cannot simply request that DOD issue a new one, or conduct a Periodic Reinvestigation, simply to make your job-hunting prospects easier. To be issued a clearance, or to renew your clearance by DOD, your present duties/assignment, or pending duties/assignment must require such access."