March Madness explained: how the NCAA tournament bracket works

March Madness is the NCAA Division I basketball tournament, held each spring for both men's and women's teams. It is single elimination: lose once and you are out. Millions of people fill out a bracket predicting every game, often without knowing exactly how the field is picked or why a team ends up as a No. 12 seed.

The format is changing in 2027. Both tournaments grow from 68 to 76 teams, and the First Four is replaced by a larger Opening Round. This guide explains how the bracket works under the new format, as of October 2026.

The short version

• Starting in March 2027, the men's and women's tournaments each have 76 teams, up from 68. The NCAA approved the change in May 2026.
• Conference champions get automatic bids. A selection committee picks the rest, called at-large teams, and seeds everyone on Selection Sunday, which is March 14, 2027.
• Twenty-four teams play a 12-game Opening Round, which replaces the First Four. The 12 winners join 52 other teams to make a bracket of 64.
• The 64 teams are split into four regions, each seeded 1 to 16. In the first round, No. 1 plays No. 16, No. 2 plays No. 15 and so on.
• The four region winners meet at the Final Four. In 2027 the men's Final Four is at Ford Field in Detroit on April 3 and 5, and the women's is at Nationwide Arena in Columbus, Ohio, on April 2 and 4.

How teams get in

There are two ways into the field.

Automatic bids. Each Division I conference gets one automatic bid, which goes to the winner of its conference tournament. A small conference champion with a modest record is in, while a strong team that lost in its conference tournament has to wait for an at-large bid.

At-large bids. The selection committee fills the remaining spots with the best teams that did not win their conference tournaments. It looks at each team's full résumé, including results against strong opponents, strength of schedule and the NCAA's NET ranking. Expanding to 76 teams adds eight at-large spots to each tournament.

The teams just outside the field are often called the "first four out" and "next four out," and the debate over them is a big part of Selection Sunday.

Selection Sunday and seeding

On Selection Sunday, the committee ranks every team in the field from top to bottom. That full list is often called the S-curve. It then places teams into four regions, so that each region has one No. 1 seed, one No. 2 seed, and so on down to the lowest lines.

When placing teams, the committee also tries to:

• Keep the regions roughly balanced in strength
• Keep teams from the same conference from meeting in the early rounds
• Send higher seeds to sites closer to home where possible

In recent years the men's regions have been the East, South, Midwest and West. In 2027, the women's regional rounds are played at two sites, Philadelphia and Las Vegas, with two regions at each.

The committee also sets which regions meet in the national semifinals, so the top overall seeds are kept apart until the Final Four.

The Opening Round (formerly the First Four)

From 2011 to 2026, the tournament opened with the First Four: four games in Dayton, Ohio, between the four lowest-seeded automatic qualifiers and the four lowest-seeded at-large teams.

From 2027, the Opening Round has 12 games and 24 teams:

• Six games between automatic qualifiers: the 12 lowest-seeded conference champions. They are eight No. 16 seeds and four No. 15 seeds.
• Six games between at-large teams: the 12 lowest-seeded at-large teams. They are four No. 11 seeds and eight No. 12 seeds.

Automatic qualifiers play other automatic qualifiers, and at-large teams play other at-large teams. On the men's side, the games are on Tuesday and Wednesday, March 16 and 17, 2027, with six in Dayton and six at a second site. The women's Opening Round is on March 17 and 18.

One practical effect: on Selection Sunday, only 20 of the 32 first-round matchups are fully known. The other 12 each wait on an Opening Round winner, and every No. 16 seed and No. 12 seed in the main bracket will have come through the Opening Round.

The 64-team bracket, round by round

After the Opening Round, each region has 16 teams, and the first-round pairings are the same in every region:

• 1 vs. 16 and 8 vs. 9
• 5 vs. 12 and 4 vs. 13
• 6 vs. 11 and 3 vs. 14
• 7 vs. 10 and 2 vs. 15

From there the rounds are:

1. First round (64 teams)
2. Second round (32 teams)
3. Sweet 16, the regional semifinals
4. Elite Eight, the regional finals
5. Final Four, the national semifinals
6. National championship

With the Opening Round included, a 76-team tournament takes 75 games to produce one champion. For the 2027 men's tournament, the first round is March 18 and 19, the second round March 20 and 21, the Sweet 16 March 25 and 26 and the Elite Eight March 27 and 28. The women's Sweet 16 and Elite Eight run from March 26 to 29.

Filling out a bracket

A few things are worth knowing before you fill one in:

• Check your pool's deadline. Many pools lock at the first tip-off of the first round, after the Opening Round is finished, so you can see who advanced.
• Look at injuries and recent form, not just seeds. A seed reflects the whole season, and a team playing without a key player in March is a different team.
• Know how your pool scores. Many give more points for later rounds, which makes your Final Four and champion picks matter more than any single early upset.

Frequently asked questions

How many teams are in March Madness?

Starting in 2027, 76 teams in both the men's and women's tournaments. From 2011 to 2026 the men's field had 68 teams, and the women's field also had 68 from 2022 to 2026.

What happened to the First Four?

It has been replaced by the Opening Round. Instead of four games between eight teams, the Opening Round has 12 games between 24 teams, played on the Tuesday and Wednesday after Selection Sunday.

What does a No. 1 seed mean?

It means the selection committee ranked that team among the top four in the field. Each of the four regions has one No. 1 seed, and in the first round it plays a No. 16 seed that came through the Opening Round.

When is Selection Sunday in 2027?

March 14, 2027, for both the men's and women's tournaments.

If you follow a college team or the whole tournament, Get Your Sports Here can send a short daily email on the teams and players you pick, with every fact linked to its source. The site keeps the schedule for everything you follow, and before a big game you can make a one-page game sheet with projected lineups, who's out and recent form. For where March fits in the rest of the year, see the year in sport calendar, or set up a briefing here.