Betting odds guide
How betting odds work, explained.
Odds tell you two things: how much a bet pays and how likely the bookmaker thinks the result is. This guide covers decimal, fractional and American odds, how to convert between them, implied probability, the bookmaker's margin and why prices move.
The basics
Three formats, one price
Decimal, fractional and American odds are just different ways of writing the same price. Switching format never changes what a bet pays. The examples below all use a stake of 10 units.
Decimal odds
The number shows your total return for each 1 unit staked, including the stake. At 2.50, a 10-unit bet returns 25: your 10 back plus 15 profit. Return = stake × odds.
Fractional odds
The fraction shows profit relative to stake. At 5/2 you win 5 for every 2 staked, so 10 units wins 25 profit and returns 35 in total. Profit = stake × fraction, then add the stake back.
American odds
Also called moneyline odds. A plus number is the profit on a 100 stake: +150 means 10 units wins 15. A minus number is what you must stake to win 100: at -200, 10 units wins 5 and returns 15.
The formulas
| From | To decimal | Example |
|---|---|---|
| Fractional (a/b) | (a ÷ b) + 1 | 5/2 → 2.5 + 1 = 3.50 |
| American, plus (+A) | (A ÷ 100) + 1 | +150 → 1.5 + 1 = 2.50 |
| American, minus (-A) | (100 ÷ A) + 1 | -200 → 0.5 + 1 = 1.50 |
| Decimal to American | 2.00 or more: (d − 1) × 100, shown with a plus | 3.00 → +200 |
| Decimal to American | Under 2.00: −100 ÷ (d − 1) | 1.25 → −400 |
Convert
Odds converter and conversion table
Type a price into any box and the other formats update. Fractions can be entered as 5/2 or "evens".
Odds converter
Common prices compared
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.20 | 1/5 | -500 | 83.3% |
| 1.25 | 1/4 | -400 | 80.0% |
| 1.33 | 1/3 | -300 | 75.0% |
| 1.50 | 1/2 | -200 | 66.7% |
| 1.67 | 4/6 | -150 | 60.0% |
| 1.80 | 4/5 | -125 | 55.6% |
| 1.91 | 10/11 | -110 | 52.4% |
| 2.00 | 1/1 (evens) | +100 | 50.0% |
| 2.50 | 6/4 | +150 | 40.0% |
| 3.00 | 2/1 | +200 | 33.3% |
| 3.50 | 5/2 | +250 | 28.6% |
| 4.00 | 3/1 | +300 | 25.0% |
| 5.00 | 4/1 | +400 | 20.0% |
| 6.00 | 5/1 | +500 | 16.7% |
| 11.00 | 10/1 | +1000 | 9.1% |
Some decimals are rounded. 1.33 is really 1.333, 1.67 is 1.667 and 1.91 is 1.909, which is why they match 1/3, 4/6 and 10/11 exactly. 6/4 is the same price as 3/2.
What the odds imply
Implied probability and the bookmaker's margin
Every price carries a probability. Implied probability = 1 ÷ decimal odds. At 4.00 that's 1 ÷ 4 = 0.25, or 25%. If you think a result is more likely than the price implies, the odds look generous to you; if less likely, they look short.
The overround
Add up the implied probabilities of every outcome in a market and the total is over 100%. The extra is the overround, and it's how a bookmaker builds in its margin.
A fair price
With no margin, a true 50/50 event would be priced at 2.00 on both sides. Bookmakers price it lower, for example 1.90 each, so they keep a share whichever side wins.
Why it matters
The margin varies by sport, market and bookmaker. Lower margins mean more of the money staked comes back to bettors over time. The same is true of multiples, where the margin compounds with every leg.
A two-way example
| Outcome | Odds | Implied probability | Fair odds (margin removed) |
|---|---|---|---|
| Team A wins | 1.90 | 52.6% | 2.00 |
| Team B wins | 1.90 | 52.6% | 2.00 |
| Total | 105.3% | 100% |
The book adds up to 105.3%, an overround of about 5.3%. Put another way, if equal amounts are staked on each side, the bookmaker keeps about 5% of the total. To strip the margin out, divide each implied probability by the total: 52.6 ÷ 105.3 = 50%.
Reading the market
Odds-on, odds-against and why odds move
Odds-on
Shorter than evens: below 2.00, such as 1/2 or -200. The bookmaker rates the result as more likely than not, and you win less than your stake.
Evens
2.00, 1/1 or +100. You win the same amount you staked, and the implied probability is 50%.
Odds-against
Longer than evens: above 2.00, such as 3/1 or +300. The result is rated less likely than not, and a win pays more than your stake.
News
Team news, injuries, line-ups and weather all change how likely a result is. Prices react, often within minutes.
Money
When a lot of money comes in on one side, bookmakers shorten that price and lengthen the other to manage their risk. A price getting shorter is "shortening"; one getting longer is "drifting".
In-play events
During a match, goals, cards and the clock move prices constantly. A team leading late on will be heavily odds-on.
The price you get is the one shown when your bet is accepted. If odds change as you place it, the site will usually ask you to accept the new price.
Odds and offers
Where odds show up in bonus terms
Welcome offers and promotions often set rules based on odds. Knowing the formats makes the terms easier to read.
- Minimum odds. Qualifying bets often need odds of at least a set price, such as 1.50 (1/2). A bet at shorter odds may not count. See wagering requirements for how these rules work.
- Check the format. If terms say 1/2 and your account shows decimals, that's 1.50. Use the converter above if unsure.
- Free bet returns. Winnings from a free bet usually exclude the stake. A 10-unit free bet at 3.00 normally returns 20, not 30. Our free bets guide explains more.
- Multiples. Some offers count each leg's odds, others the combined odds. Our bet types guide covers how combined odds are worked out.
- Asian lines. Handicap and totals markets with quarter lines can settle as half wins or half losses. See Asian handicap explained.
- Before you cash out. Withdrawals usually need your account to be verified. See withdrawals and ID checks.
Good to know
Betting odds FAQ
What does evens mean?
Evens is a price of 2.00 in decimal, 1/1 in fractional and +100 in American odds. You win the same amount you stake, so a 10-unit bet returns 20 in total. The implied probability is 50%.
Which odds format is best?
None of them pays more than the others. They are different ways of writing the same price. Decimal odds are the simplest for working out returns, and most betting sites let you switch format in your account settings.
What does a minus sign mean in American odds?
A minus number shows how much you need to stake to win 100 profit, so the selection is odds-on. At -200 you stake 200 to win 100, which is the same as 1.50 in decimal or 1/2 in fractional odds.
How do I work out implied probability?
Divide 1 by the decimal odds and multiply by 100. At 4.00, 1 divided by 4 is 0.25, so the implied probability is 25%. Convert fractional or American odds to decimal first.
Why do the probabilities add up to more than 100%?
Bookmakers build a margin into their prices, called the overround. If both sides of a 50/50 market are priced at 1.90 instead of 2.00, the implied probabilities add up to about 105.3%, and that extra is the bookmaker's edge.
Check you're eligible. Whether you can bet online, and which sites you can use, depends on the laws where you live and each bookmaker's own terms. This guide is general information only and isn't a recommendation. Odds are never a guarantee of any result. 18+ only. Please gamble responsibly, and see our responsible gambling page if betting stops being fun.