This week, Major League Baseball released the schedule for the 2015 season. You may have noticed that it starts later and ends later than previous seasons—but each team still plays 162 games, just as they have for decades. But how did MLB arrive at such a seemingly arbitrary number?

Let's start in 1920. There was baseball before then, but that's when both the National and American Leagues settled on a season length that would hold for over 40 years. At the time, it was simple math: two leagues of eight teams each—there were no divisions yet—meant each team had seven rivals. For a few years, teams had played each of their rivals 20 times for a 140-game season. In 1920, this was expanded to 22 games against each of seven rivals, 11 at home and 11 away, resulting in an 154-game season.

Then, leagues started expanding. In 1961, the American League added the Los Angeles Angels and the Washington Senators. The following year, the National League welcomed the New York Mets and the Houston Colt .45's. "After the first expansion, each team had nine rivals rather than seven, and the 154-game season made for bad math," MLB's official historian, John Thorn, explains. To play 22 games against each rival would require an 198-game season, so MLB settled on 18 games per rival for nine rivals, for a total of 162 games.

(Thorn clarifies that yes, in 1961, after the AL had expanded but the NL had not, the leagues played seasons of different lengths. "Both World Series contestants opened their regular seasons on April 11 and concluded on October 1," he says. "NL had more days off.")

The season has been 162 games ever since, but it's taken some work to keep it there. "Even with further expansions, 162 became the de facto standard, and you had to get more and more complicated arithmetically to make it work," Thorn says. "So when we went to two 6-team divisions [per league] in 1969 the—I think brilliant—solution was to have more games against the teams in your division, thus enabling you to preserve the 162-game season."

The addition of a third division in each league in 1994, introduction of interleague-play in 1997, a final expansion to 30 teams total in 1998 and, most recently, the realignment of the leagues that necessitated perpetual interleague games last season has made for increasingly complicated scheduling and yet the season holds at 162 games.

These days, teams play 76 contests against division rivals, 66 against non-division league teams, and 20 interleague games—or 162 games. It works, but it feels a little random. The reason the schedule has stayed at 162 games is largely because to change it would be so difficult.

"No one wants to give up home dates," Thorn says. "So if we went to 158 games, each team would have to give up two home dates and that’s revenue." Meanwhile, a longer season would mean ending even later in the year than the late October/early November World Series of late. And unless the teams agreed to play at a warmer, neutral location (unlikely given, again, the potential hit to ticket sales) this could result in some seriously cold weather at the championship games.

It's not just the bureaucratic intricacies that have kept the season length consistent (although trying to imagine the MLB Players Association and the team owners reaching an agreement to ever add or subtract a single game is probably explanation enough). Baseball is, after all, a sentimentalist's game. "Baseball is a religion," Thorn says. "It becomes the 11th commandment: 162 games."