CERTIORARI TO THE SUPREME COURT OF FLORIDA.
Marshall, J., delivered the opinion of the Court, in which Brennan, Stewart, White, Powell, and Stevens, JJ., joined. Blackmun, J., filed an opinion concurring in the judgment, in which Burger, C. J., joined, post, p. 36. Rehnquist, J., filed an opinion concurring in the judgment, post, p. 37.
JUSTICE MARSHALL delivered the opinion of the Court.
Florida, like many other States, rewards each convicted prisoner for good conduct and obedience to prison rules by using a statutory formula that reduces the portion of his sentence that he must serve. In this case, we consider whether a Florida statute altering the availability of such "gain time for good conduct"*fn1 is unconstitutional as an ex post facto law when applied to petitioner, whose crime was committed before the statute's enactment.
The relevant facts are undisputed. Petitioner pleaded guilty to second-degree murder. The crime charged occurred on January 31, 1976. On May 13, 1976, petitioner was convicted and sentenced to a prison term of 15 years, less time
already served. The state statute in place on both the date of the offense and the date of sentencing provided a formula for deducting gain-time credits from the sentences "of every prisoner who has committed no infraction of the rules or regulations of the division, or of the laws of the state, and who has performed in a faithful, diligent, industrious, orderly and peaceful manner, the work, duties and tasks assigned to him." Fla. Stat. § 944.27 (1) (1975).*fn2 According to the formula, gain-time credits were to be calculated by the month and were to accumulate at an increasing rate the more time the prisoner had already served. Thus, the statute directed that the authorities "shall grant the following deductions" from a prisoner's sentence as gain time for good conduct:
"(a) Five days per month off the first and second years of his sentence;
"(b) Ten days per month off the third and fourth years of his sentence; and
"(c) Fifteen days per month off the fifth and all succeeding years of his sentence." Fla. Stat. § 944.27 (1) (1975).
In 1978, the Florida Legislature repealed § 944.27 (1) and enacted a new formula for monthly gain-time deductions. This new statute provided:
"(a) Three days per month off the first and second years of the sentence;
"(b) Six days per month off the third and fourth years of the sentence; and
"(c) Nine days per month off the fifth and all succeeding years of the sentence." Fla. Stat. § 944.275 (1) (1979).*fn3
The new provision was implemented on January 1, 1979, and since that time the State has applied it not only to prisoners sentenced for crimes committed since its enactment in 1978, but also to all other prisoners, including petitioner, whose offenses took place before that date.*fn4
Petitioner, acting pro se, sought a writ of habeas corpus from the Supreme Court of Florida on the ground that the new statute as applied to him was an ex post facto law prohibited by the United States and the Florida Constitutions.*fn5 He alleged that the reduced accumulation of monthly gain-time credits provided under the new statute would extend his required time in prison by ...