On April 30, 2014, the United States Sentencing Commission submitted to Congress an amendment to the federal sentencing guidelines that would revise the guidelines applicable to drug trafficking offenses by changing the base offense levels in the Drug Quantity Table in section 2D1.1 of the Guidelines Manual. The commission has released a report analyzing the impact of the guideline amendment if made retroactive. It has also released a report of the Recidivism Among Offenders Receiving Retroactive Sentence Reductions: The 2007 Crack Cocaine Amendment.
Federal prisoners currently can earn up to only 47 days off of their sentences each year if they follow prison rules and are well-behaved. A good time table is available here.
A bill pending before Congress, the Recidivism Reduction and Public Safety Act of 2013, would increase the amount of good time from 47 days to 54 days per year.