There is a general expectation or even assumption (albeit mistaken) that once a judge awards presentence credits for time served in a local facility (county jail) that such credits cannot be reduced or lost. This general expectation is misplaced when a person on probation commits a serious of violent felony that constitutes a probation violation. When this type of probation violation takes place and the person is sent off to state prison, rather than county jail, presentence credits are reduced from 4-for-2 (50% credit) to 8-for-7 (15% credit). This can be a big shock to most people. To read about an actual case where this took place and was challenged, click on the following link.