The American Gaming Association noted that the $35 billion estimate represents roughly a 30 percent increase over the amount wagered on the NFL last year, and is based on data released by some states on total wagers on professional football. The Colorado Division of Gaming, for example, reported $890.3 million wagered on “professional football” in fiscal year 2023/2024.

Three states -- Maine, North Carolina and Vermont -- have launched legal betting markets since the most recent NFL season. Overall, 38 states plus the District of Columbia have legal betting markets in place heading into the NFL season.

Sportsbooks say that, on a per-game basis, more money is wagered on the NFL than any other league. The NFL also attracts the largest bets, with six- and seven-figure bets being reported on an almost weekly basis by U.S. sportsbooks.

"The NFL typically produces the largest bets not only because of the popularity of the league, but also the schedule," Johnny Avello, director of sportsbook for DraftKings, told ESPN in an email. "Single games tend to attract more significant bets, and the NFL has more single games in the regular season than any other league. That creates a lot of excitement and attracts quite a few notable bets."

The pregame point spread remains the most popular betting option in the NFL, along with money lines (odds of winning the game) and over/under totals, according to sportsbooks. 

Christian Cipollini, commercial manager for BetMGM sportsbooks, noted that point spread, money line and over/under total about 50 percent of bets surrounding an NFL game, with proposition bets, both team and player, and alternate markets making up the remaining 50 percent. Cipollini estimates that "60-65 percent" of NFL bets are made before kickoff, but added that "live betting is growing."

The odds to win the Super Bowl attract more betting interest than any other league championship. BetMGM said it has received twice as many bets on the winner of the upcoming Super Bowl as it has on the winner of the upcoming World Series. DraftKings also revealed that the Super Bowl leads the way in terms of betting interest.

"It's evidence of the NFL's popularity, and ability to keep fans and bettors engaged all year long," Avello said.

The NFL season kicks off Thursday, with the defending champions of the past two Super Bowls, the Kansas City Chiefs, hosting the Baltimore Ravens.