In federal sentencing, the judge determines the ultimate sentence an individual receives after looking at various factors, including the individual’s personal history, the crime and conduct of which they have been convicted, and the Federal Sentencing Guidelines manual (which provides a suggested sentencing guideline range in every case).
The sentencing normally happens seventy days after a person is found guilty, whether by guilty plea or after a conviction at trial. If the judge orders a sentence longer than twelve months, the individual is eligible for good time credit of up to 15 percent off the total, as long as there have been no disciplinary problems.
The United States Sentencing Commission promulgates the Sentencing Guidelines manual and usually amends it every year. The current version of the Guidelines manual can be found here.