Held: Lee has demonstrated that he was prejudiced by his counsel’s erroneous advice. Pp. 5–13.(a) When a defendant claims that his counsel’s deficient performance deprived him of a trial by causing him to accept a plea, the defendant can show prejudice by demonstrating a “reasonable probability that, but for counsel’s errors, he would not have pleaded guilty and would have insisted on going to trial.” Hill v. Lockhart, 474 U. S.52, 59. Lee contends that he can make this showing because he never would have accepted a guilty plea had he known the result would be deportation. The Government contends that Lee cannot show prejudice from accepting a plea where his only hope at trial was that something unexpected and unpredictable might occur that would lead to acquittal. Pp. 5–8. (b) The Government makes two errors in urging the adoption of a per se rule that a defendant with no viable defense cannot show prejudice from the denial of his right to trial. First, it forgets that categorical rules are ill suited to an inquiry that demands a “case-by-case examination” of the “totality of the evidence.” Williams v. Taylor,529 U. S. 362, 391 (internal quotation marks omitted); Strickland,466 U. S., at 695. More fundamentally, it overlooks that the Hill v. Lockhart inquiry focuses on a defendant’s decisionmaking, which may not turn solely on the likelihood of conviction after trial. The decision whether to plead guilty also involves assessing the respective consequences of a conviction after trial and by plea. See INS v. St. Cyr, 533 U. S. 289, 322–323. When those consequences are, from the defendant’s perspective, similarly dire, even the smallest chance of success at trial may look attractive. For Lee, deportation after some time in prison was not meaningfully different from deportation after somewhat less time; he says he accordingly would have rejected any plea leading to deportation in favor of throwing a “Hail Mary” at trial. Pointing to Strickland, the Government urges that “[a] defendant has no entitlement to the luck of a lawless decision maker.”466 U. S., at 695. That statement, however, was made in the context of discussing the presumption of reliability applied to judicial proceedings, which has no place where, as here, a defendant was deprived of a proceeding altogether. When the inquiry is focused on what an individual defendant would have done, the possibility of even a highly improbable result may be pertinent to the extent it would have affected the defendant’s decision making. Pp. 8–10. (c) Courts should not upset a plea solely because of post hoc assertions from a defendant about how he would have pleaded but for his attorney’s deficiencies. Rather, they should look to contemporaneous evidence to substantiate a defendant’s expressed preferences. In the unusual circumstances of this case, Lee has adequately demonstrated a reasonable probability that he would have rejected the plea had he known that it would lead to mandatory deportation: Both Lee and his attorney testified that “deportation was the determinative issue” to Lee; his responses during his plea colloquy confirmed the importance he placed on deportation; and he had strong connections to the United States, while he had no ties to South Korea. The Government argues that Lee cannot “convince the court that a decision to reject the plea bargain would have been rational under the circumstances,” Padilla v. Kentucky, 559 U. S. 356, 372, since deportation would almost certainly result from a trial. Unlike the Government,this Court cannot say that it would be irrational for someone in Lee’s position to risk additional prison time in exchange for holding on to some chance of avoiding deportation. Pp. 10–13.825 F. 3d 311, reversed and remanded. ROBERTS, C. J., delivered the opinion of the Court, in which KENNEDY,GINSBURG, BREYER, SOTOMAYOR, and KAGAN, JJ., joined. THOMAS, J., filed a dissenting opinion, in which ALITO, J., joined except as to Part I. GORSUCH, J., took no part in the consideration or decision of the case.