How does March Madness work?

The NCAA Division I men's basketball tournament fields 68 teams. Conference tournament champions receive automatic bids, and a selection committee chooses the remaining at-large teams and seeds the entire field from one to sixteen across four regions. Eight teams play in the First Four to reduce the field to 64, after which the bracket is single elimination through the round of 64, round of 32, Sweet Sixteen, Elite Eight, Final Four, and championship game. The women's tournament follows the same structure and has grown substantially in viewership, having been permitted to use the March Madness branding only since 2022 after an external review found significant disparities in how the two tournaments were resourced.

The bracket is the cultural phenomenon. Filling one out requires predicting 63 games, and the probability of a perfect bracket by coin flip is one in roughly 9.2 quintillion. Applying knowledge improves the odds dramatically but leaves them remote, with commonly cited estimates around one in 120 billion for an informed picker. No verified perfect bracket has ever survived beyond the second round in the era of large-scale online tracking, and the longest documented run ended partway through the Sweet Sixteen in 2019.

Upsets are the engine. Higher seeds are favored but 12 over 5 upsets occur with enough regularity to be a betting cliché, and 16 over 1 has happened twice on the men's side, first in 2018 and again in 2023. The financial context is substantial and increasingly contested: the tournament generates the large majority of NCAA revenue through media rights, which sat alongside the amateurism model that restricted athlete compensation until name, image, and likeness rules changed in 2021 and subsequent litigation and settlements moved college sports toward direct revenue sharing with athletes.