I would like to know the meaning of this sentence.

Your confusion is understandable. Your son was apparently convicted of a crime with a minimum mandatory sentence of 10 years- was a gun involved? Assuming that he has 3 years time served against a 15 year sentence for a remainder of 12 years, Florida law requires that an inmate serve 85% of their sentence. The 85% is of what is sentenced, not of the sentence after any credit for time served is deducted. Thus, someone sentenced to 15 years must serve 12.8 years, minus what time they have actually already served. In your son's case, if he was credited with 3 years time served (which is a huge amount- are you sure that this is correct?), he will have to still serve 9.8 years. The 10 years minimum mandatory varies slighlty depending on the exact offense, as the Florida legislature is not always consistent in how it drafts minium mandatory sentences. Assuming that this is a true minimum mandatory, then he is not eligible to earn any gain time for the first 10 years of his sentence, but it can be credited against the last five. Gain time is discretionary with the DOC and can be taken away for various infractions.  Gain time is governed by F.S. §944.275. Florida Administrative Code Rule 33-601.101 lays out how the DOC handles gain time. Both are available for free online. Because gain time can be earned and lost, no definite release date can be given at this time for your son. The DOC should establish an earliest possible release date- which may be the 2026 number to which you refer - and a maximum release date.  All of the above assumes that there are no changes in the law. Florida is one of a very few states with an accross-the-board minimum as high as 85% and no parole. It has been this way for quite a while, so I do not anticipate any changes, but I have been surprised before. Good luck, Michael R. Morris