There is no universal rule that every federal prisoner serves exactly 85 percent of the imposed sentence inside a prison. Good-conduct time, prior-custody credit, First Step Act credits, and authorized release programs involve different rules. A reliable estimate starts with the judgment and the Bureau of Prisons computation. [1]
What good-conduct time does
Section 3624 generally allows eligible prisoners serving more than one year, other than life, up to 54 days of good-conduct credit per year of the sentence imposed. The credit depends on statutory requirements and satisfactory behavior. That maximum produces the familiar approximation, but it is not an automatic reduction for every sentence. [1]
A sentence of exactly one year presents a different eligibility issue from one year and one day. Lost disciplinary credit and computation details can also affect the actual release date. Do not assume an online percentage calculator accounts for them.
First Step Act credits are separate
Eligible participation in qualifying programs or productive activities can earn time credits under section 3632. Earning credits and applying them are different steps. Conviction-based exclusions, risk assessments, participation, and other statutory conditions can affect eligibility and use. [2]
Applied credits may concern prerelease custody or earlier supervised release under the governing rules. Home confinement or a residential reentry center is not simply the same thing as an unconditional end to the sentence.
Other provisions, including qualifying residential drug treatment, can involve separate discretionary benefits. Not every participant receives a reduction, and a program’s name does not establish eligibility. [3]
Example: two similar judgments
Two people with equal prison terms may have different projected dates because one has creditable presentence custody, different disciplinary history, or different statutory credit eligibility. Comparing only the judge’s announced number misses those variables.
Obtain the judgment, custody timeline, sentence-computation record, disciplinary decisions, and credit information. Identify whether a disputed date is the release-from-custody date, transfer to prerelease custody, or start of supervised release.
Raise a computation issue through the appropriate BOP process and preserve supporting records. A court challenge has its own procedural requirements. Treat an estimate as provisional until the responsible authority verifies the actual calculation; transfers and program projections should not be represented as guaranteed release dates.
A focused example appears in a 24-month federal sentence. The punishment decision itself occurs at the federal sentencing hearing.
Primary sources
- 18 U.S.C. § 3624: Release of a prisoner
- 18 U.S.C. § 3632: Development of risk and needs assessment system
- 18 U.S.C. § 3621: Imprisonment of a convicted person
Sources checked: October 31, 2026.