From a NY Times piece.

Alan and Karen Miller’s first dance was a win-or-lose moment for many of their wedding guests.

As the couple glided across the floor during their reception in New Rochelle, N.Y., last year, attendees kept track of the chosen artist and the length of the dance. Earlier in the night, they had noted their guesses on prop bet sheets.

Proposition, or prop, bets are usually tied to sporting events. Users place wagers on specific details that aren’t necessarily correlated with a game’s outcome, like points scored by certain players. Now, these bets have entered the world of weddings.

More couples have been integrating betting into their celebrations in recent years through digital apps or printed cards. While the Millers, who live in New York City, aren’t avid sports bettors or gamblers themselves, they wanted to make their June 2025 celebration more interactive and distinctive for their 175 guests....

Stacy and Greg Stahl, from St. Louis, have spent almost 10 years betting on various aspects of their friends’ weddings — from who would say the vows first to whether the ceremony would last longer than 20 minutes — just for the fun of it.

“It started with a certain friend group,” Stacy said. “We started betting at that first friend’s wedding, and since then, we bet at every subsequent wedding of that friend group. By the end of it, we were including almost everyone in the wedding, including the father of the bride, the uncles and so much of the extended family.”

In 2023, the couple decided to turn this pastime into a business and developed Betting on the Wedding, an interactive app that allows guests to make predictions by answering premade or custom questions.

The Stahls said that more than 25,000 couples so far had created a betting pool using their app, which costs a one-time fee of $49.99.

Guests can monitor the status of their bets on their phones via a live leaderboard throughout the wedding. At the end of the event, the app sends a notification to all participants letting them know how they performed and, if applicable, whom they may owe money to....