In Georgia - a misdemeanor sentence can range from probation to 1 year in jail. Each county sheriff determines credit to be given to inmates who serve "good time" with no infractions.
Jails I am familiar with often grant 'trustee' status to inmates who exhibit good behavior with no infractions. Often, these inmates will be given special work details outside of the facility and other benefits. Generally, these inmates will receive 2 days credit towards their sentence for every day spent incarcerated. Other inmates may serve every day of their sentence.