Judge Randall Wyatt issued a written order Tuesday on the sentencing of Cyntoia Brown.
He sentenced her to 20 years on the especially aggravated robbery charge, to run concurrent with the life sentence she received.
Brown was found guilty in August of killing real estate agent Johnny Allen. The first-degree murder charge carries a life sentence, and under Tennessee law, the defendant must serve at least 51 years before being eligible for parole.
Brown was 16 years old when she shot Allen to death in 2004.