Legal Question in Criminal Law in California

Your calculations are incorrect. If he was sentenced to a year in jail and has been in custody since October 8, he won't hit the halfway (six-month) mark until April.

The state courts are still trying to figure out how to interpret the change in the law, which went into effect on January 25, 2010, and there is a bill in the Legislature to change it back.

As things stand today, he probably won't get half time credit (actually two days for every two days served) for any time served before January 25. Instead, he would get two days for every four served.

He may not even be eligible for half time under the new law. From your question, I can't figure out his exact charges, but it he was convicted of felony witness intimidation under California Penal Code 136.1, he is ineligible for half time. He would also be ineligible for half time if he has a prior "strike" felony conviction or if he is a registered sex offender.

Like almost everyone else today, jails use computers for record keeping. Although computers can make mistakes (usually because someone enters the wrong information), they are a lot more accurate than trying to keep track of inmates' release dates with a bunch of papers or index cards.