18 U.S.C. § 4105

(a) Except as provided elsewhere in this section, an offender serving a sentence of imprisonment in a foreign country transferred to the custody of the Attorney General shall remain in the custody of the Attorney General under the same conditions and for the same period of time as an offender who had been committed to the custody of the Attorney General by a court of the United States for the period of time imposed by the sentencing court. (b) The transferred offender shall be given credit toward service of the sentence for any days, prior to the date of commencement of the sentence, spent in custody in connection with the offense or acts for which the sentence was imposed. (c) (1) The transferred offender shall be entitled to all credits for good time, for labor, or any other credit toward the service of the sentence which had been given by the transferring country for time served as of the time of the transfer. Subsequent to the transfer, the offender shall in addition be entitled to credits toward service of sentence for satisfactory behavior, computed on the basis of the time remaining to be served at the time of the transfer and at the rate provided in section 3624(b) of this title for a sentence of the length of the total sentence imposed and certified by the foreign authorities. These credits shall be combined to provide a release date for the offender pursuant to section 3624(a) of this title . (2) If the country from which the offender is transferred does not give credit for good time, the basis of computing the deduction from the sentence shall be the sentence imposed by the sentencing court and certified to be served upon transfer, at the rate provided in section 3624(b) of this title . (3) Credit toward service of sentence may be withheld as provided in section 3624(b) of this title . (4) Any sentence for an offense against the United States, imposed while the transferred offender is serving the sentence of imprisonment imposed in a foreign country, shall be aggregated with the foreign sentence, in the same manner as if the foreign sentence was one imposed by a United States district court for an offense against the United States.