Allen rejected a two-year, $12 million offer to return to the Boston Celtics and accepted a three-year deal with the Miami Heat, who were limited to their mid-level exception amount of slightly more than $3 million per season. During Allen's first season with the Miami Heat, he averaged 10.9 points per game and made 88.6% of his free throws while playing an average of 25.8 minutes per game. On April 25, 2013, while playing Milwaukee in Game 3 of the first round of the playoffs, Allen made his 322nd career three-pointer in the playoffs, which broke Reggie Miller's record for most three-pointers made in NBA playoff history. Allen returned to his favorite #34 jersey upon joining the Heat.