In 2013, the Houston Astros joined the American League, giving each league 15 teams and thereby necessitating that interleague games be played throughout the season, including on Opening Day and during key division races all the way to the end of the season. This did not require expanding the total number of interleague games, because the probability of an interleague game during the era in which the Astros played in the NL was 252/2430 or about 1 in 9.6 games (this number is not an integer because not all teams had the same number of interleague games). With an odd number of teams in each league, one team in each league would be the "odd man out" and have to play an interleague game to fill out the schedule, meaning as few as 1 in 15 games could be interleague (14 AL teams in 7 AL games, 14 NL teams in 7 NL games and 1 AL and 1 NL team in an interleague game). Despite this, there have been proposals to increase interleague play to 30 games. While the increase to 30 games is highly unlikely for the foreseeable future, a smaller increase took place immediately, having every team play 20 interleague games.