Do they have two for one days served in other correctional prisons?

It is a fairly common practice. In the US State of Georgia, you get two days credit off your sentence for every day in custody prior to conviction.

Different jurisdictions have different programs. Remember when Lindsay Lohan was released early a couple times? One time she was released hours after booling, another she served 13 days of a 90 day sentence. In those cases, the sheriff let her go to relieve overcrowding.

From what I know of the county system around here, you start off at half the time of your sentence. For instance, if they sentence you to a year, you get six months. Your release date is six months away, minus any time already served.

But that other (unused) six months is leverage against you. It’s still part of your sentence, but it’s “good behavior” time—meaning if you’re good, you get out after the first six months. But if you’re found doing any bad behavior (such as lifting a metal spoon from the day room, which is contraband), some of those “good” days are docked. In other words, your release date is postponed so that in effect time is added. That spoon could cost you two days. That way they don’t have to change your sentence, just the amount of it that you serve.