Day v. McDonough, 547 U.S. 198 (2006), is a US Supreme Court case involving the one-year statute of limitations for filing habeas corpus petitions that was established by the Antiterrorism and Effective Death Penalty Act of 1996 (AEDPA).

A US magistrate judge nevertheless acknowledged that the petition was "in proper form" and ordered Florida to file an answer and to make all arguments regarding Day's potential failure to exhaust state remedies or procedural default.

In his objection to the report and recommendation of the magistrate judge, Day argued for the first time that the concession of timeliness by the state was dispositive because it was a forfeiture of that defense.

Justice Ruth Bader Ginsburg delivered the opinion for the majority in holding that district courts are permitted but not obliged to consider sua sponte the timeliness of a state prisoner's habeas corpus petition.

The Court instead agreed with the State of Florida, which argued that "[t]he considerations of comity, finality, and the expeditious handling of habeas proceedings that motivated AEDPA...counsel against an excessively rigid or formal approach to the affirmative defenses" such as the statute of limitations.

The Court observed that the State could have simply amended its answer had the Magistrate Judge informed it of its computation error rather than acting sua sponte.

Courts must also ensure that the petitioner is not significantly prejudiced by the delayed focus on the limitation issue, and "determine whether the interests of justice would be better served" by addressing the merits or by dismissing the petition as time barred.

In that case, however, the Court believed the Magistrate Judge gave Day due notice and a fair opportunity to show why the limitation period should not yield dismissal of the petition, and there was nothing to suggest that the State "strategically" withheld the defense or chose to relinquish it.

The Court had recently granted certiorari in Lawrence v. Florida,[7] a case which would answer the question of whether Day's petition was actually barred by the statute of limitations.

He suggested that the lower court may still avoid a "miscarriage of justice" by keeping Day's case on its docket until after Lawrence is decided, "but it would be better practice for us to do so ourselves."

Scalia, joined by Breyer and Clarence Thomas, objected that the Court was disregarding the clear provisions of the Federal Rules of Civil Procedure (FRCP), which required the forfeiture of affirmative defenses when they are not raised.

Scalia considered it most important that no provision of the habeas statute would be contradicted or undermined by applying the forfeiture rule to the limitations period.

Given the "background understanding" that failure to raise the defense of limitations constitutes waiver, "the statute implies that the usual forfeiture rule is applicable."

Scalia distinguished the other affirmative defenses to habeas petitions as having been created as judicial doctrines by the courts, "in the exercise of their traditional equitable discretion, because they were seen as necessary to protect the interests of comity and finality that federal collateral review of state criminal proceedings necessarily implicates."

The Court's observation that there was no substantive difference between allowing the State to amend its answer and simply dismissing sua sponte was characterized by Scalia as "what appears to be the chief ground of its decision."