((a)) ** Full registration period** A sex offender shall keep the registration current for the full registration period (excluding any time the sex offender is in custody or civilly committed) unless the offender is allowed a reduction under subsection (b). The full registration period is—

((1)) 15 years, if the offender is a tier I sex offender;

((2)) 25 years, if the offender is a tier II sex offender; and

((3)) the life of the offender, if the offender is a tier III sex offender.

((b)) ** Reduced period for clean record**

((1)) ** Clean record** The full registration period shall be reduced as described in paragraph (3) for a sex offender who maintains a clean record for the period described in paragraph (2) by—

((A)) not being convicted of any offense for which imprisonment for more than 1 year may be imposed;

((B)) not being convicted of any sex offense;

((C)) successfully completing any periods of supervised release, probation, and parole; and

((D)) successfully completing of  an appropriate sex offender treatment program certified by a jurisdiction or by the Attorney General.

((2)) ** Period** In the case of—

((A)) a tier I sex offender, the period during which the clean record shall be maintained is 10 years; and

((B)) a tier III sex offender adjudicated delinquent for the offense which required registration in a sex registry under this subchapter, the period during which the clean record shall be maintained is 25 years.

((3)) ** Reduction** In the case of—

((A)) a tier I sex offender, the reduction is 5 years;

((B)) a tier III sex offender adjudicated delinquent, the reduction is from life to that period for which the clean record under paragraph (2) is maintained.