42 USC 16915 - Duration of registration requirement

(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[1] 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 title, 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.
[1] So in original. The word “of” probably should not appear.