<P> Perhaps the biggest key to the tremendous popularity of the tournament is the bracket . The March Madness bracket is the grid of all the teams in the tournament and the path they have to follow to the Final Four and the championship game . Filling out a bracket with the winners of each of the 67 games in the tournament is an incredibly difficult task, and nobody has successfully filled out a perfect bracket . Odds of a perfect bracket are estimated to be 1 in 9,223,372,036,854,775,808 (9.2 quintillion). Some March Madness contests are free to enter, others require an entry fee . Many businesses utilize pool hosting services to run their pools, allowing them the flexibility to customize the pool rules and display . </P> <P> March Madness has become one of the most popular sporting events in the United States . Because of the length of the tournament and the number of teams involved it is one of the most popular sporting events in terms of television ratings . One event associated with March Madness is filling out the brackets . It has become extremely common in popular culture even among non-sports fans . It is estimated that millions of Americans participate in the contest every year . Mainstream media outlets such as ESPN, CBS Sports and Fox Sports host tournaments online where contestants can enter for free . Employers have also noticed a change in the behavior of employees during this time . They have seen an increase in the number of sick days used, extended lunch breaks and even the rescheduling of conference calls to allow for more tournament watching . There are also many handicappers and pundits which offer advice for winning your bracket . </P>

When can you start filling out brackets for march madness