The difference is huge, because a defendant who serves offenses concurrently serves time for the different crimes at the same time. In other words, if a defendant was convicted of two crimes, he or she would not have to serve one sentence and then another—the sentences would both run as soon as the defendant was in prison.

On the other hand, a defendant who serves sentences consecutively must serve one sentence before the next sentence begins. This means that consecutive sentencing keeps the defendant in prison for much longer than concurrent sentencing.