Good conduct time, good time credit, or time off for good behavior is a sentence reduction given to prisoners who maintain good behavior while imprisoned. Good time can be forfeited if a prisoner is determined to have committed disciplinary infractions and/or crimes while incarcerated.
Under United States federal law, prisoners serving more than one year in prison get 54 days a year of good time on the anniversary of each year they serve plus the pro rata good time applied to a partial year served at the end of their sentence, at the rate of 54 days per year. At the same time, however, the calculation cannot be applied in such a way as to extinguish the anniversary of time served because this would lead to the absurdity that a full good time credit was given without the prisoner actually demonstrating the required exemplary behavior throughout the full term of one year.
This complexity is easily clarified with two examples. A prisoner sentenced to 18 months' imprisonment (say 548 days) will receive the 54 days' credit upon serving the first 365 days, reducing his time for that year to 311 days, with 183 days (six months) to serve, total time overall of 494 days at that point. If maintaining exemplary behavior thereafter, the remaining 183 days will be reduced by 27 days (one year pro rata) resulting in 156 days only to be served in the second year, i.e. a final overall total of 467 days. Here it can be seen that the inmate enjoys a 14.8% discount on time served.
Prisoners on sentences just a little over a year, however, do not enjoy the same discount. A prisoner sentenced to 13 months' imprisonment (say 395 days) cannot serve less than 365 days because it is only upon completion of that year that the required exemplary conduct for the whole year has been fulfilled by the inmate and the 54-day benefit vested. Thus, this prisoner will be released upon the anniversary, having enjoyed a 54-day credit which has extinguished the remaining 30 days (one month) of the term. In this example, the discount, therefore, is only 7.5%.
Persistent controversy over calculation of good conduct time in the United States was laid to rest in the Supreme Court decision in Barber v. Thomas in 2010.
Rumors constantly circulate within federal prisons that a Good Time Bill will be passed increasing the amount of good time granted to prisoners, and indeed such bills are sometimes introduced.