PORTLAND — A state prison inmate has lost his bid to have the law court order an additional two days of good-time credit per month during the entire time he is serving his sentence.

Glen C. Harrington III, 30, formerly of Fairfield, challenged the prison policy in an appeal argued in May before the justices of the Maine Supreme Judicial Court. Harrington’s petition to get that credit had been summarily dismissed at a Superior Court proceeding.

According to the appeal, Harrington believed that when he pleaded guilty to eluding an officer in Kennebec County in 2012, he would be eligible to take classes at the Maine State Prison to reduce his sentence.

But he soon learned that program is offered only to inmates within 18 months of release, so he challenged the Department of Corrections.

At oral arguments in May, the justices seemed reluctant to interfere with Department of Corrections operations.

And in the decision issued Tuesday, Maine Supreme Court Associate Justice Joseph Jabar wrote, “Calculations of good time credits involve the department’s discretion in either determining whether an inmate’s participation in a specific program has merited good time credit or, as is the case here, whether and when to offer a program.”

The state, represented at oral arguments by Assistant Attorney General Diane Sleek on behalf of the Kennebec County district attorney, maintained that Harrington should have used a different appeal process – not post-conviction review – to file his dispute over the calculation of his good-time credits.

On Wednesday, District Attorney Maeghan Maloney said she was pleased with the court’s decision and deliberations, adding, “The Department of Corrections has established a set policy for good-time calculations that was applied to Mr. Harrington in the same manner it does to every person housed at the department.”

Harrington’s lawyer, James T. Lawley, said Wednesday he and his client are disappointed by the decision.

Lawley said Wednesday that he notified Harrington of the decision by mail. Harrington is serving a 48-month term. His earliest release date is Dec. 15, 2015, according to Department of Corrections website.