Sports betting has its own vocabulary and three different ways to write the same price. This guide explains the most common terms and shows how to read decimal, fractional and American odds. Betting is a risk, not an investment. There are no guaranteed winners, and bookmakers build a margin into their prices.
Odds formats
Decimal odds
Common in Europe, Australia and Canada. The number shows the total return per 1 unit staked, including your stake. At 2.50, a 10 unit bet returns 25 if it wins: 15 profit plus your 10 back.
Fractional odds
Traditional in the UK and Ireland. They show profit relative to stake. At 3/2 you win 3 for every 2 staked. A 10 unit bet at 3/2 gives 15 profit and a 25 total return. The same price as decimal 2.50.
American (moneyline) odds
Used in the US. A positive number shows how much profit you make on a 100 stake: +150 means 150 profit on 100. A negative number shows how much you must stake to win 100: -200 means you stake 200 to win 100. Underdogs are usually positive, favourites negative.
Converting between formats
Decimal 2.50 equals fractional 3/2 equals American +150. Decimal 1.50 equals fractional 1/2 equals American -200. Most betting sites let you switch the display format in settings, so you never have to convert by hand.
Implied probability
Odds can be turned into a probability. In decimal odds, divide 1 by the price: 1 / 2.50 = 0.40, or 40%. This is the chance the price implies. Because of the bookmaker’s margin, the implied probabilities across all outcomes add up to more than 100%.
Bet types
- Single
- One selection, one bet.
- Moneyline (match winner)
- A bet on who wins outright.
- Point spread or handicap
- A bet where one side is given a head start or deficit to even out the contest.
- Over/under (totals)
- A bet on whether the combined score or count is above or below a number.
- Parlay or accumulator
- A single bet combining several selections. All must win for the bet to pay. The potential return is bigger, but so is the risk, because one loss sinks the lot.
- System bet
- A set of smaller combinations built from several selections, which can still pay if some lose.
- Each-way
- A bet split into a win part and a place part, used mainly in horse racing.
- Prop bet
- A wager on a specific event within a game, such as a player statistic.
- Futures
- A bet on a result that will be decided in the future, such as a league winner.
- Live or in-play betting
- Betting while the event is underway, with odds that change quickly.
- Cash out
- An option to settle a bet early for an amount offered by the bookmaker.
Other words you will see
- Stake
- The amount you bet.
- Favourite and underdog
- The side the market thinks most or least likely to win.
- Margin (vig, juice, overround)
- The built-in bookmaker advantage in the odds.
- Bookmaker or sportsbook
- The business taking your bet.
- Void
- A bet cancelled with the stake returned, for example when an event is called off.
- Push
- A tie against the spread or total, usually returning your stake.
- Free bet
- A promotion that gives you a bet without using your own money. Terms vary: in many cases only the winnings, not the stake, are returned.
- Steam or line movement
- Changes in the odds over time, often caused by news or betting volume.
A short worked example
You bet 20 at decimal 3.00 on a team to win. If it wins, the total return is 20 x 3.00 = 60, which is 40 profit plus your 20 stake. If it loses, you lose the 20. Now add a second selection at 2.00 in an accumulator with the same 20 stake: both must win, and the total return would be 20 x 3.00 x 2.00 = 120. Notice the higher return depends on winning twice, which is less likely than winning once.
Before you place any bet
Check the rules of the market, confirm the odds format and stake, and only bet what you can afford to lose. If a bet feels urgent, step away for a few minutes.
Reading a betting slip
A slip normally lists your selection, the market, the odds, your stake and the potential return. Check each line before confirming, especially the market. Betting on “over 2.5 goals” is a different bet from “exactly 3 goals”, and an odds format shown in fractions can look like a different price from the same odds in decimals. Errors on a confirmed bet usually cannot be undone.
Where the bookmaker’s margin hides
If a coin toss really is 50-50, fair decimal odds for each side would be 2.00. A bookmaker might offer 1.91 on both sides. The implied probabilities then add up to a little above 100%, and that surplus is the margin. It means that even if you are right about a fifty-fifty outcome half the time, you will lose money over many bets. Comparing prices across licensed bookmakers is the simplest way to reduce that cost.
Staying in control
- Set a betting budget and never chase losses.
- Be careful with accumulators, cash out offers and in-play betting, which can encourage fast, emotional decisions.
- Use deposit limits and time-outs offered by licensed sportsbooks.
- Check that the bookmaker holds a licence in your region.
Bookmakers use many of the same terms as casinos. For those, see our casino glossary. For bonus and free bet language, read our bonus terms glossary. If you enjoy card games, our poker glossary covers that vocabulary.
18+ (21+ where local law requires) only. Play responsibly. Gambling involves risk and no strategy or guide can guarantee a win. Only play with money you can afford to lose. If gambling stops being fun, see our responsible gambling page for tools and helplines.