Spread betting is any of various types of wagering on the outcome of an event, where the pay-off is based on the accuracy of the wager, rather than a simple "win or lose" outcome, which is known as money-line betting. A spread is a range of outcomes, and the bet is whether the outcome will be above or below the spread. Spread betting has been a major growth market in the UK in recent years, with the number of gamblers heading towards one million. As with all gambling, however, spread betting carries a high level of risk. In the UK, spread betting is regulated by the Financial Services Authority rather than the Gambling Commission.

Purpose

The general purpose of spread betting is to create an active market for both sides of a wager, even if the outcome of an event may appear a priori to be biased towards one side or the other. In a sporting event, for example, a strong team may be pitted against a historically weaker team. Persons betting on the event normally would be likely to favor the better team, to such an extent that there would be very few, if any, betting on the team perceived to be worse.

The use of a "point spread" evens out the market towards an equal number of participants on each side of the wager. This allows a bookmaker to make a market by accepting wagers on both sides of the spread. The bookmaker charges a commission and acts as the counterparty for each participant. As long as the number of participants on each side is roughly equal, the bookmaker is unconcerned with the actual outcome; profits instead come from the commissions.

Spreads in sports wagering

Spread betting was invented by Charles K. McNeil, a mathematics teacher from Connecticut who became a bookmaker in Chicago in the 1940s. The idea became popular in the United Kingdom in the 1980s. In North America, the gambler usually wagers that the difference between the scores of two teams will be less than or greater than the value specified by the bookmaker. An example:

• The bookmaker advertises a spread of 4 points in a certain game;
  • If the gambler bets on the "underdog", he is said to take the points and will win if the underdog's score plus the spread is greater than the favourite's score.
    • The eventual score is Underdog 8, Favorite 10: 8 + 4 > 10, so the gambler wins;
    • The eventual score is Underdog 8, Favorite 13: 8 + 4 < 13, so the gambler loses.
    • The eventual score is Underdog 4, Favorite 10: 10 - 4 > 4, so the gambler wins;
    • The eventual score is Underdog 8, Favorite 10: 10 - 4 < 8, so the gambler loses.