The most time you get off your sentence in the federal system is 54 days per year of imprisonment [0]. That's nearly a 7:1 ratio. If he's sentenced to 14 years for example, he'd only get 2 years off for "good behavior," thus serving 12 instead of 14.

0: https://www.kohlerandhart.com/blog/2023/03/15/how-is-good-be...