The Bowl Championship Series, a set of four college football bowl games that rotate the honor of hosting the #1-vs.-#2 national championship game. The "BCS formula" is a ranking system mainly designed to decide the teams to participate in this championship game.

The BCS formula takes into account five data sources. The first four are the average of eight computer ratings (dropping the lowest and highest for each team), the average ranking between the coaches' poll and the AP poll, number of losses, and strength of schedule (itself a complex formula involving total wins and losses for both the team's direct opponents and the opponents' opponents). The last source is the ranking produced by the first four factors; wins over teams ranked in the top 15 of this ranking are rewarded by subtracting points from the total (the "quality win" component).

The formula is only consulted for two reasons, though -- to decide #1 and #2 for the rotating MNC game, and to determine at-large eligibility for teams that did not win automatic bids from the BCS conferences (Big East, Atlantic Coast Conference, Big Ten, Big Twelve, Pacific-10, and Southeastern Conference). The top twelve teams in the BCS ratings are eligible for the two at-large spots; one at-large spot can be automatically earned by any independent or non-BCS conference team by finishing with a top-six rating. If that happens, Notre Dame can automatically earn the other at-large spot with either nine wins or a top-10 rating.

When a BCS game is not hosting the national championship game, it has first call on the champion from its designated home conference(s) (if those teams don't make the NC game). Home assignments are:

  • Rose Bowl: Big Ten and Pac-10
  • Fiesta Bowl: Big Twelve
  • Sugar Bowl: SEC
  • Orange Bowl: Big East or ACC (cannot automatically claim both; must select one as automatic, then pick the other in the at-large picking order for the year).

Source for eligibility information: