The amount of time, if any, a person will spend in jail for a DUI conviction depends on the number of prior DUI convictions and the circumstances of the current offense.
Whether a DUI conviction will lead to jail depends on a number of circumstances. In many states—including Florida and Pennsylvania—jail time isn't mandatory (though it is possible) for a standard first DUI conviction where no one was injured or killed.
Even in states where jail time is mandatory for a first DUI conviction, the offender can sometimes avoid having to actually serve the time in jail by doing house arrest, community service, or some other alternative sentencing option.
A number of states require one or more days jail for a second or subsequent DUI offense. For instance, New Hampshire doesn't mandate jail time for a first DUI but requires at least 17 days in jail for a second DUI conviction. And even in states where jail time isn't required by law for repeat offenders, judges almost always have the option, which they often exercise, of sentencing a motorist convicted of a second or subsequent DUI to serve time in jail.
The bottom line is that the likelihood of spending time in jail goes up substantially when you have prior DUI convictions.
Apart from prior convictions, lots of other factors can increase the likelihood of spending time behind bars for a DUI conviction. These factors might include accidents (especially when they involve injuries, death, or substantial property damage), a high blood alcohol concentration (BAC), and having minors in your vehicle at the time of a DUI offense.
Whatever the circumstances of your case, it's a good idea to talk to an experienced DUI attorney as soon as possible. A qualified DUI lawyer can tell you how the law applies to your situation and help you decide on the best course of action.