my boyfriend was sentenced to 6 years . how much time will he actually do of that?

He will do 85% of 72 months or 61.2 months... about 5 years. This 15% is good time credited at the beginning of his bid, he can only screw up and lose that. If he is federal, there is a drug program that will shave off 12 months for successful completion. There are few other ways to gain an earlier release aside from snitching. The government rewards snitches with early release.