The American Gaming Association forecasts that 1 in 5 American adults will place a bet on Sunday’s NFL championship game between the Philadelphia Eagles and the Kansas City Chiefs.

The estimate includes legal bets, and those placed with illegal bookies or casually among friends or relatives.

The total amount expected to be wagered this year is more than double the amount from last year as the legal U.S. sports betting market continues to grow.

There are three additional states offering legal sports betting this year — Kansas, Ohio and Massachusetts — compared with a year earlier, for a total of 33 states plus Washington, D.C. Maryland also added mobile sports betting in the past year, but it had in-person wagering for last year’s Super Bowl.

More than half of all American adults live in a market where sports betting is legal.

“Every year, the Super Bowl serves to highlight the benefits of legal sports betting: Bettors are transitioning to the protections of the regulated market, leagues and sports media are seeing increased engagement, and legal operators are driving needed tax revenue to states across the country,” said Bill Miller, the association’s president and CEO.

Hard data is backing up predictions of a record-setting betting market for this year’s game. GeoComply, which handles nearly all the online betting traffic for the U.S. sports betting market to verify a customer is in a particular location where such bets are legal, says it has recorded over 550 million geolocation checks during the NFL playoffs from Jan. 14 to 29.

That’s up 50% from the same period last year, and the group is predicting record-setting volume for this year’s Super Bowl.

Eilers & Krejcik Gaming Research, an independent analytics firm in California, looked solely at legal bets. It predicted a total of just over $1 billion this year, led by Nevada ($155 million); New York ($111 million); Pennsylvania ($91 million); Ohio ($85 million) and New Jersey ($84 million.) Their research was not involved in the AGA predictions.

The company estimated 10 to 15% of that total would be wagered live after the game begins, and that 15 to 20% would come in the form of same-game parlays, or a combination of bets involving the same game, such as betting on the winner, the total points scored and how many passing yards Eagles quarterback Jalen Hurts will accumulate.

The AGA survey found bettors evenly split, with 44% backing the Chiefs and an identical percentage betting on the Eagles.

The Eagles were 1.5-point favorites as of Monday night on FanDuel, the official odds provider to The Associated Press.

There is a vast array of bets offered on the big game, from the most basic predictions of which team will win and by how many points, to wagering on the total amount of points scored in the game.

Also popular are so-called proposition or prop bets on individual player performances, like whether Chiefs quarterback Patrick Mahomes will throw two or fewer touchdown passes or how many rushing yards Eagles running back Miles Sanders will accumulate.

For the Super Bowl, these bets encompass outcomes as unusual as whether the opening coin toss will come up heads or tails; whether the final score of the game has ever happened before as the score of a past Super Bowl, and even what color of Gatorade will be dumped on the winning coach.