HOW THE SYSTEM WORKS — COMPUTATION

Federal Sentence Computation Explained

A federal release date is not a single number a judge sets — it is the output of a computation the Bureau of Prisons runs, layering prior custody credit, good conduct time, and First Step Act credits onto the sentence imposed. Understanding how that math is built is what lets a family tell whether the date is right.

LAST REVIEWED: July 5, 2026 · FEDERAL SYSTEM ONLY · EDUCATIONAL — NOT LEGAL ADVICE

TIME LEDGER — CASE FILE SUMMARY READ THE COMPUTATION

Who computes it	The BOP, not the sentencing judge
Prior custody credit	Time in custody before sentencing, under 18 U.S.C. §3585(b)
Good conduct time	54 days per year of sentence imposed, §3624(b)
FSA time credits	Programming credits under §3632(d)(4)
Concurrent vs consecutive	How multiple sentences combine, set by the judgment
Where to read it	The sentence-monitoring computation and FSA assessment

The judge sets the sentence; the BOP builds the date

A common misunderstanding is that the judge sets the release date. The judge sets the sentence imposed — the number of months — and the Bureau of Prisons then computes the actual dates by applying the credits and adjustments the law requires. That division of labor is why so many errors are the BOP's to fix, not the court's, and why the administrative remedy program is usually the right first venue.

The computation is a document you can read. It shows the sentence imposed, the date it began, prior custody credit, projected good conduct time, and — since the First Step Act — an FSA time-credit assessment. Learning to read it is the foundation for catching mistakes, which is what our release-date guide teaches step by step.

Prior custody credit — the time already served

Under 18 U.S.C. §3585(b), a person generally gets credit for time spent in official detention before the sentence began, as long as that time was not already credited against another sentence. For someone who sat in pretrial detention for months, this can be substantial — and it is a frequent source of error, especially where state and federal custody overlapped or where the timeline is tangled.

Because the BOP computes this credit, disputes about it go to the BOP first. Families should map the custody timeline carefully — every date the person was detained, and by whom — because prior custody credit errors can hide months. Where custody overlapped with a state case, the analysis gets intricate and rewards careful documentation.

Good conduct time — the near-automatic reduction

The next layer is good conduct time: up to 54 days for each year of the sentence imposed, under §3624(b). The First Step Act settled a long-running dispute about how to calculate it so that the full 54 days per year is credited. Good conduct time is nearly automatic, lost only through the disciplinary process, and it drives the projected release date on most computations.

A family reading a computation should be able to see the projected good conduct time and confirm it matches 54 days per year with no unexplained forfeitures. A disciplinary sanction that took good conduct time should be traceable to a specific incident report and hearing.

First Step Act credits — the earned layer

On top of good conduct time sit First Step Act credits, earned through programming and applied under §3624(g). These behave differently from the automatic reductions: they must be earned, they are subject to the exclusion list, and they apply first to the release date (up to 365 days) and then to prerelease custody without cap.

Because FSA credits and good conduct time are separate, they appear separately, and confusing them is the most common computation error families make. Our guide comparing FSA credits and good conduct time untangles exactly how the two layers combine.

Concurrent vs. consecutive — when there's more than one sentence

When a person has multiple sentences — federal counts, or a federal and a state term — how they combine is decisive. Sentences run concurrently (at the same time) or consecutively (one after another), and the judgment controls which. A term the judgment makes consecutive adds its full length; a concurrent term overlaps. Getting this relationship wrong can swing a release date by years.

The interaction of federal and state sentences is especially technical, involving questions of primary jurisdiction and whether the federal term was ordered to run concurrently with an existing or anticipated state term. Detainers from other jurisdictions add another layer. Where multiple sentences are involved, the computation deserves especially careful review.

Reading the whole sheet

Put together, the computation is a stack: sentence imposed, minus prior custody credit, minus projected good conduct time, minus applied FSA credits, adjusted for how multiple sentences combine — yielding the projected release date and, separately, the prerelease-custody dates. A family that can identify each layer can spot where a number is wrong.

The audit questions follow the layers: Is prior custody credit complete? Is good conduct time the full 54 per year? Are FSA credits earned, applied, and reflected? Do multiple sentences combine as the judgment ordered? Our calculator checks the FSA layer independently, and when something is off, the miscalculation guide and remedy program are how you fix it.

Frequently asked questions

Who calculates a federal release date?

The Bureau of Prisons, not the sentencing judge. The judge sets the sentence imposed in months; the BOP then computes the actual dates by applying prior custody credit, good conduct time, and First Step Act credits. That's why computation errors are generally the BOP's to fix, through the administrative remedy program.

What is prior custody credit?

Under 18 U.S.C. §3585(b), credit for time spent in official detention before the sentence began, as long as it wasn't already credited against another sentence. For someone held in lengthy pretrial detention it can be substantial, and it's a frequent source of error where state and federal custody overlapped.

How do good conduct time and FSA credits fit into the computation?

They're separate layers. Good conduct time is up to 54 days per year of the sentence imposed and is near-automatic. First Step Act credits are earned through programming and applied on top — up to 365 days to the release date and, beyond that, to prerelease custody. Confusing the two is a common error.

Why does having two sentences complicate the math?

Because sentences run either concurrently (at the same time) or consecutively (one after another), and the judgment controls which. A consecutive term adds its full length; a concurrent one overlaps. Federal-state combinations involve primary jurisdiction and detainers, and errors here can swing a release date by years.

Free consultation

Want this applied to a specific case? Get My Days Back was founded by someone who served federal time. The first conversation is free, and we will tell you plainly if the free guides on this site already cover what you need.

Request a free consultation →