The amount of time actually served on a custodial sentence in California depends on the current offense, and the offender's past record (if any).
Law Offices of David Shapiro 3555 4th Avenue San Diego, CA 92103 (619) 295-3555
No all sentences get 2 for 1 good time credits. Depending on the charges some crimes require 70-80% of time. As for violations, can be sentenced to whatever remainder of imposed time was.
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This is too complicated of a question with too many unknown variables for any of us to give you a thorough answer here. I strongly suggest consulting with a local criminal defense attorney. Good luck.