WASHINGTON, Jan 13 (Reuters) - Federal inmates who successfully participate in recidivism-reduction programs will qualify for early release from prison under new rules unveiled on Thursday by the U.S. Justice Department. The rules, mandated by Congress in a 2018 federal law called the First Step Act, allow inmates to earn 10 to 15 days of "time credits" shaved off their sentence for every 30 days of participation in certain programs or activities offered to them by the federal Bureau of Prisons (BOP). By earning those credits, they can qualify to be released early into halfway houses or home confinement. In some cases, inmates can also earn up to 12 months of credit that would be applied toward supervised release. The new rule will apply retroactively, allowing inmates to earn credits from prior participation in programs since Dec. 21, 2018, when the First Step Act became law. The Justice Department faced criticism over its original proposal on how it would implement the federal time credits rule, with federal defenders saying the Bureau of Prisons" menu of available programs was too limited and the number of hours required to complete them would make it too hard for inmates to earn credits. "The math speaks for itself," federal defenders wrote in a January 2021 letter to the bureau. "It would take 219 weeks, or over 4 years to earn a full year of credit under the BOP"s proposed rule." Criminal justice advocates who lobbied for the First Step Act"s passage lauded the new finalized rule on Thursday, saying it is now in line with what Congress intended. "Today"s announcement is relief for thousands of people who have done the hard work to turn their lives around, and rejoin their families and communities as productive, law-abiding citizens," Holly Harris, the president of Justice Action Network, said in a statement.