A landmark Supreme Court ruling could see around 500 prisoners have their release dates brought forward.
Yesterday's ruling will see 21 prisoners walk free today, Corrections chief executive Ray Smith confirmed in a statement today.
"Corrections has always followed the lawful rulings of the Court in its calculation of sentence release dates," Mr Smith said.
He said on four previous occassions, the Court of Appeal had upheld Corrections' practices in calculating pre-sentence detention.
Approximately 500 prisoners will have their release dates brought forward.
"In most cases this will only be by a matter of a few days or weeks rather than a significant period of time," Mr Smith said.
Corrections must now recalculate the sentences of affected prisoners in light of the ruling.
Corrections made a mistake
The Supreme Court said in a judgement released yesterday that the Department of Corrections made a mistake when it calculated the release date for two prisoners, Michael Marino and Edward Booth.
An appeal by the two men concerned how Corrections has been factoring in the time already spent in detention when calculating parole and release dates.
Both men spent a long period in jail on remand, but Corrections failed to factor that in when calculating their release.
The Supreme Court decision means sentences have to be counted from the moment someone is taken into custody, even for extra charges imposed after that initial arrest.
Source: ONE News
Corrections had only been counting time spent in custody towards the initial charge.
The court unanimously held that the Parole Act has been misinterpreted and as a consequence, in some instances - including those involving the appellants - parole and release dates have been calculated on the wrong basis.