How Release Dates Are Calculated in Illinois

If you or someone you love is doing time in Illinois, the release date depends on one key question: which tier of the truth in sentencing law applies. Illinois uses determinate sentencing, meaning the court sets a specific term and the Department of Corrections calculates release based on that sentence and the sentence credits the person earns. For nonviolent offenses, those credits can cut the sentence in half. For serious violent offenses, the law requires serving at least 85 percent. For first degree murder, the full sentence is served.

This guide walks through how Illinois calculates a release date step by step: the four-tier credit structure and what drives each one, how sentence credits are earned and lost, Mandatory Supervised Release as the post-prison supervision period, and the recent changes from 2018 and 2024. None of this is legal advice, but it will help you read your own time the way the Illinois Department of Corrections does.

Here is the short version.

Illinois has four service tiers set by the truth in sentencing law. Most nonviolent offenses are on the day for day tier, where sentence credits reduce the prison term by up to half. Class X drug delivery offenses involving more than 100 grams of a controlled substance sit at the 75 percent tier, but earned program and education credits can bring that down to 60 percent. A range of serious violent offenses fall in the 85 percent tier, where program credits can be earned but the floor stays at 85 percent. First degree murder is at 100 percent, with no credits of any kind. Everyone released from Illinois prison goes on Mandatory Supervised Release for a period set by the felony class.

Step one: determinate sentencing and the four tiers

Illinois moved from indeterminate sentencing and parole to determinate sentencing in February 1978. Under determinate sentencing, the court sets a specific term and that number drives everything. The amount of the sentence that must actually be served in prison is then governed by which truth in sentencing tier applies to the offense.

The four tiers are written into Illinois statute and determine the minimum percentage of the sentence that must be served before the Department of Corrections can release a person. The tier is set by the offense of conviction, not by behavior in prison or the judge's preferences. Knowing the tier is the first step in understanding any Illinois release date.

Illinois also eliminated the old parole system when it moved to determinate sentencing. The Illinois Prisoner Review Board handles Mandatory Supervised Release supervision and violations, but it does not grant parole to end prison time early. Release date is calculated by the Department of Corrections based on the sentence and the applicable tier.

Step two: the day for day tier, how it works

The day for day tier applies to most nonviolent offenses in Illinois and is the most favorable credit structure in the system.

Under the day for day tier, a person receives one day of sentence credit for each day of service in prison. This effectively cuts the sentence in half: a four-year sentence results in two years served in prison. Before Illinois passed its truth in sentencing law in 1998, nearly all sentences worked this way. Today, nonviolent offenses still operate under this structure.

Sentence credits on the day for day tier can be earned in additional ways beyond the basic day for day calculation. Credits are available for full participation in substance abuse programs, educational programs, correctional industry assignments, work release, behavior modification programs, life skills courses, and re-entry planning. Each qualifying day of program participation earns a day of credit. These earned program and education credits stack on top of the baseline credit, and families should know that active participation in programming directly affects how much of the sentence is actually served in prison.

Good time can also be lost. Illinois allows IDOC to revoke sentence credits for serious disciplinary violations, and a revocation pushes the release date later. A significant violation can erase days or weeks of earned credit, which is why maintaining good conduct matters in a very concrete way.

Step three: the 85 percent tier, serious violent offenses

A range of serious violent offenses in Illinois fall under the 85 percent tier, which means at least 85 percent of the court-imposed sentence must be served in prison.

The offenses included in this tier cover the most serious violent crimes apart from first degree murder: among others, attempted first degree murder, solicitation of murder, predatory criminal sexual assault, aggravated criminal sexual assault, criminal sexual assault, armed robbery, aggravated kidnapping, aggravated vehicular hijacking, aggravated battery with a firearm, and numerous offenses that have been added to the list since the original 1998 law, including Armed Habitual Criminal, Aggravated Domestic Battery, and Aggravated DUI resulting in death or bodily harm. The statutory list has grown over time through legislation.

Since 2018, Illinois law allows people serving 85 percent sentences to earn certain program and education credits. However, those credits cannot reduce the time served below the 85 percent floor. In practice, this means earning program credits at the 85 percent tier does not change the release date if the person is already slated to serve exactly 85 percent. The floor is the floor.

For a ten year sentence at the 85 percent tier, the minimum prison time is eight and a half years. No amount of programming or good behavior reduces that number. What good conduct does do on the 85 percent tier is prevent the loss of any credits and protect against revocation that could push the date later than the 85 percent mark.

Step four: the 75 percent tier and the 60 percent floor

A specific category of Class X drug offenses occupies its own tier in Illinois, and it has a more flexible structure than the 85 percent tier.

Class X felony drug delivery offenses involving more than 100 grams of a controlled substance are subject to a 75 percent service requirement. However, since 2017 through a change that took effect in 2018, people serving sentences in this category can earn earned discretionary sentence credits and earned program and education credits that reduce the floor down to 60 percent. The exception is gunrunning, which stays at 75 percent regardless of credits earned.

What this means practically is that someone on a ten year sentence for a qualifying Class X drug delivery offense must serve at least seven and a half years but can, through consistent program participation, get down to six years. Earning the maximum credits requires active engagement in approved programming throughout incarceration.

The 60 percent floor in this tier represents a significant reward for rehabilitation. It is also worth knowing that the offense must qualify, meaning the weight threshold of more than 100 grams of a controlled substance must be part of the conviction, not simply a Class X felony.

Step five: the 100 percent tier, first degree murder

First degree murder in Illinois carries a 100 percent service requirement, meaning the full sentence imposed by the court is served in prison with no sentence credits of any kind.

There are no credits, no good time, no program reductions, and no mechanism that shortens the sentence for a first degree murder conviction. Someone sentenced to 30 years for first degree murder serves 30 years. The truth in sentencing law is absolute on this point.

Natural life sentences are served for the natural life of the person, with no possibility of release absent a pardon or commutation from the Governor.

For sentences where the death penalty was imposed and later commuted, or where other unusual sentence structures exist, the Department of Corrections determines the applicable service requirement based on the specific judgment. Anyone with questions about a specific sentence structure should request the time computation directly from the Department.

Step six: Mandatory Supervised Release

When a person is released from Illinois prison at the point required by their tier, they do not simply walk free. Everyone released from IDOC is placed on Mandatory Supervised Release for a period determined by the felony class of the offense.

Mandatory Supervised Release is the Illinois equivalent of parole supervision. It is administered by the Illinois Prisoner Review Board, which sets conditions and monitors compliance. The MSR period runs after the prison term is complete. During MSR, a person must follow conditions set by the Board, report regularly to a parole agent, and comply with restrictions. Violations of MSR conditions can result in a hearing before the Board and a return to prison to serve additional time.

The MSR period depends on the felony class: Class X offenses typically carry three years of MSR; Class 1 felonies typically carry two years; Class 2, 3, and 4 felonies carry shorter periods. Specific offenses may carry different MSR terms set by the statute defining the offense. Starting January 1, 2024, completing an educational or vocational program during incarceration reduces the MSR period by 90 days.

Families planning for release need to plan for MSR as an active part of the sentence. It is not optional, it carries real conditions, and a violation means a return to prison.

Putting it together: a worked example

Here is how the pieces fit, using simple examples. None of these numbers are legal advice, but they show the method.

Take a four-year sentence for a nonviolent Class 2 felony. The day for day tier applies. At one day of credit per day served, the person is released at two years if all credit is maintained and no credits are revoked for violations. Active program participation earns additional credits beyond the baseline, potentially shortening the prison term further. After release at or before two years, the person goes on Mandatory Supervised Release for the period applicable to Class 2 felonies.

Now take a ten year sentence for armed robbery. Armed robbery falls in the 85 percent tier. The minimum time in prison is eight and a half years, and no programming or good conduct reduces that floor. At eight and a half years, the person is released to Mandatory Supervised Release for the period applicable to the offense class.

Finally, take a 30-year sentence for first degree murder. The 100 percent tier applies. Thirty years are served in full with no sentence credits of any kind. The person goes on Mandatory Supervised Release after serving the full 30 years.

The bottom line for Illinois

Illinois release dates start with identifying the tier: day for day, 75 percent toward 60, 85 percent, or 100 percent. For nonviolent offenses on the day for day tier, active program participation and clean conduct can get the prison term to half the sentence or below. For the 75 percent Class X drug tier, earned credits can bring the floor down to 60 percent. For the 85 percent violent offense tier, programming and good conduct protect the floor but do not lower it. For first degree murder, 100 percent is absolute.

The practical takeaways are clear. First, confirm which tier applies, because the tier is the most important number in the calculation. Second, if on the day for day or 75 percent tier, participate actively in programs because earned credits reduce the actual time in prison. Third, protect credits on every tier by maintaining good conduct, because revocation can push the release date later on any tier. Ask the Illinois Department of Corrections for the current release date and the credit balance so you know exactly where things stand.