Day-for-Day Credit in Illinois: Rates, Exceptions, and Revocation

Day-for-day credit in Illinois lets most people in state prison earn one day off their sentence for each day served, so a qualifying six-year sentence works out to roughly three years behind bars. The catch is that the full rate does not apply to everyone. Illinois restricts credit for first degree murder, serious violent and sexual offenses, and large-scale drug crimes, and the offense of conviction — along with the date it was committed — decides which rate you get.

The Base Rule: One Day Off for Each Day Served

Under 730 ILCS 5/3-6-3, the Illinois Department of Corrections awards one day of sentence credit for each day a person serves. That is the source of the “day-for-day” shorthand, and in practice it cuts a qualifying prison term roughly in half. A four-year sentence becomes about two years in custody; a ten-year sentence becomes about five.¹

IDOC calculates sentences using 30-day months. The record office at the receiving facility runs the initial calculation, then recalculates whenever the sentence structure changes, and every calculation goes through a two-person review before it is final.²

This base rate applies to any offense that is not on one of the restricted lists below. Burglary, theft, lower-level drug possession, and many other non-violent felonies fall into this 50% category. People serving natural life sentences receive no credit at all.¹

Offenses That Don’t Get the Full Rate

Illinois puts serious offenses on restricted tiers that cap how much credit can be earned. The differences are significant: on a ten-year sentence, the tier is the difference between serving five years and serving every day of ten.

100% — Full Sentence Required

First degree murder and terrorism carry no sentence credit at all. The person must serve the entire sentence the court imposed. This rule applies to offenses committed on or after June 19, 1998.¹

85% — Serious Violent and Sexual Offenses

Offenses in this tier earn no more than 4.5 days of credit per month, which works out to serving about 85% of the sentence. Covered offenses include:

Attempt to commit first degree murder, attempt to commit terrorism, solicitation of murder, and solicitation of murder for hire
Predatory criminal sexual assault of a child, aggravated criminal sexual assault, and criminal sexual assault
Aggravated battery of a child, aggravated battery of a senior citizen, and heinous battery
Aggravated kidnapping, aggravated battery with a firearm, and unlawful possession of a firearm by a repeat felony offender

A second group of offenses lands in the 85% tier only when the court finds the conduct caused great bodily harm to a victim. That group includes home invasion, armed robbery, aggravated vehicular hijacking, aggravated discharge of a firearm, and armed violence with a category I or II weapon.¹

75% — Large-Scale Drug Offenses

Serious drug-related offenses involving 100 grams or more of a controlled substance earn no more than 7.5 days of credit per month, meaning roughly 75% of the sentence served. This tier covers narcotics racketeering, controlled substance trafficking, methamphetamine trafficking, drug-induced homicide, and Class X delivery of controlled substances at that weight threshold.¹

Why the Offense Date Matters

Each restricted category has its own effective date, and an offense committed even a day before that date may qualify for a more favorable rate under the rules in force at the time. The core 85% list took effect for offenses committed on or after June 19, 1998. Other offenses were added later, each with its own cutoff. Aggravated domestic battery, for example, falls under the restricted rules only if the offense was committed on or after July 23, 2010.¹

When you calculate expected time served, the date on the charging document matters as much as the offense name.

Credit That Stacks on Top

Day-for-day is only one type of credit. Other categories add to it, and since 2018 some are available even to people on restricted tiers.

Program Credit

A person engaged full-time in a qualifying activity earns one additional day of credit for each day of participation. Qualifying activities include substance abuse treatment, educational and vocational programs, work-release, behavior modification courses, life skills classes, and re-entry planning. For less-than-full-time activities like volunteer work or self-improvement programs, the rate is half a day for each day of participation.¹

Educational Achievement Bonuses

Completing a degree or equivalency inside triggers a one-time credit bonus on top of any daily program credit earned along the way:

High school equivalency (GED): 90 days
Associate degree: 120 days
Bachelor’s degree: 180 days
Master’s or professional degree: 180 days

Supplemental Credit

The IDOC Director can award additional credit for good conduct, institutional service, and community service. The cap is 180 days for sentences under five years and 365 days for sentences of five years or longer. A person must serve at least 60 days, including jail time, before becoming eligible.¹

What Changed in 2018 for Restricted Tiers

Before Public Act 100-3 took effect on January 1, 2018, people convicted of offenses in the 85%, 75%, or 100% tiers were largely locked out of program-based credits. They can now earn program and supplemental credit, but the total reduction cannot push time served below a statutory floor:

85% tier: sentence cannot be reduced below 85%
75% tier: cannot be reduced below 60%, except gunrunning, which stays at 75%
100% tier: no reduction at all, regardless of programming

Someone in the 75% tier who actively participates in programming can serve as little as 60% of the sentence.³

When Credit Can Be Taken Back

Sentence credit is not permanent. Any type of credit, whether day-for-day, program, supplemental, or educational, can be revoked for disciplinary violations or rule-breaking.

IDOC can revoke up to 30 cumulative days of credit within any 12-month period on its own. If the amount at issue exceeds 30 days, or if cumulative revocations during a 12-month period would exceed that threshold, IDOC has to submit its recommendation to the Prisoner Review Board for approval.⁴

There is a separate rule for infractions close to release. When misconduct happens within 60 days of a scheduled release, IDOC can revoke up to 30 days without Prisoner Review Board involvement. Anything beyond 30 days still needs board approval.⁴

Revocations affect the projected release date, not the mandatory release date. The mandatory release date changes only when there is an actual absence from IDOC supervision, such as an escape or a release on bond.²

Prison Time Isn’t the Whole Sentence

Sentence credit shortens time in prison. It does not shorten mandatory supervised release (MSR), which every person on a determinate sentence must serve after leaving custody. MSR functions like parole, and its length depends on the felony class:

First degree murder and Class X felonies: 3 years
Class 1 and Class 2 felonies: 2 years
Class 3 and Class 4 felonies: 1 year

MSR comes with conditions set by the Prisoner Review Board, including regular reporting and travel restrictions. Violations can send someone back to prison, and time on supervision before a violation does not always count toward the remaining obligation.⁵

This is where the math often surprises people. A four-year sentence for a Class 2 felony at the 50% rate means roughly two years in prison followed by two years of MSR. That is four years under state control, not two.

1
Illinois General Assembly. Illinois Compiled Statutes 730 ILCS 5/3-6-3 – Rules and Regulations for Sentence Credit
2
Illinois Department of Corrections. Administrative Directive 01.07.400 – Sentence Calculation for Individuals in Custody
3
Illinois General Assembly. Illinois Compiled Statutes 730 ILCS 5/3-6-3 – Rules and Regulations for Sentence Credit – Section 4.7
4
Illinois General Assembly. Illinois Administrative Code Title 20 Part 107 – Sentence Credit
5
Illinois General Assembly. Illinois Compiled Statutes 730 ILCS 5 – Unified Code of Corrections – Felony Sentencing Provisions