The calculation projected actual time to be served is a complex one. It is based on the factors you provide and others. The best way to obtain an estimate is to request one from the inmate's prison counselor and then to verify it with an experienced criminal defense lawyer in the jurisdiction. Other factors that may reduce actual time to be served are "good behavior" and specific institutional policy. An example of a policy reduction is an educational or trade course credit. Also changes in the law of sentencing that may be passed by the state legislature could reduce (but not increase) the time in prison.
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Sounds like he got 15 years (3 suspended, 12 to serve) and 10 years post release supervision with 5 reporting. MDOC may let him out sooner, but the Judge ordered him to serve 12 years.
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