The Economics of Sports Betting

How bookmakers make money on odds, why the average bettor loses over time, and the debate over legal betting's benefits and harms.

Sports betting means staking money on the outcome of a sporting event, such as which team will win or how many runs will be scored. It is legal and heavily advertised in some countries and restricted or banned in others. Whatever the law, the economics are the same, and they explain a simple but important fact: over time, the bookmaker - the company taking the bets - expects to win, and the average bettor expects to lose.

Odds and implied probability

Odds tell you how much you’ll be paid if a bet wins. They also contain a hidden estimate called the implied probability - the chance of winning that the odds suggest. For example, odds that pay back 2 rupees for every 1 rupee staked (including the stake) imply a 50 percent chance.

How the bookmaker wins

A bookmaker doesn’t need to predict results perfectly. Instead, it sets odds so that the implied probabilities of all possible outcomes add up to more than 100 percent. The extra is the bookmaker’s margin, sometimes called the “vig”. It works like a built-in fee on every bet.

A coin-toss match with a margin

Imagine a match that is truly even, with each side having a 50 percent chance. Fair odds would pay back 2 rupees for every 1 rupee staked. A bookmaker might instead offer odds paying back about 1 rupee and 90 paise on each side. If one person bets 100 rupees on each team, the bookmaker collects 200 rupees and pays back 190 to whoever wins, keeping 10 rupees - about 5 percent - regardless of the result. Across many bets, that small margin adds up.

Expected value: why the average bettor loses

Expected value is the average result you’d get if you repeated a bet many times. Because of the margin, the expected value of a typical bet is negative for the bettor. Some bets win, and occasional big wins are memorable, but across many bets the losses tend to exceed the gains. Promotions like “free bets” are usually designed to encourage more betting, which increases the bookmaker’s total income.

People sometimes believe that knowing a lot about a sport lets them beat the market. A very small number of skilled bettors may succeed for a while, but bookmakers often limit or close the accounts of consistent winners.

The policy debate

Governments take very different approaches. Supporters of legal, regulated betting argue it brings illegal markets into the open, raises tax revenue and allows consumer protections. In the United States, a 2018 Supreme Court decision allowed states to legalise sports betting, and many have done so. In India, betting on sport is largely prohibited, and in 2025 Parliament passed a law banning online real-money games, while supporting other forms of gaming such as esports.

Critics point to real harms. Problem gambling can lead to debt, stress, family conflict and mental health struggles, and easy access through phone apps can make it harder to stop. Betting also creates incentives for match-fixing, which threatens the integrity of sport itself. Regulators respond with tools like age limits, spending limits, self-exclusion schemes and advertising rules.

Thinking a losing streak means a win is "due"

Each bet is independent: past losses don't make the next bet more likely to win. Chasing losses by betting more to win money back is one of the most common patterns in problem gambling. Anyone who feels betting is becoming hard to control should talk to someone they trust and seek help from a local support service.

Key takeaways

Odds carry an implied probability of each outcome winning.
Bookmakers build a margin into odds, so they profit regardless of results.
The expected value of a typical bet is negative for the bettor.
Countries differ on legalisation, weighing tax revenue and regulation against problem gambling and match-fixing.