What this guide covers
Every other guide on this site assumes you can read a price. This one shows you how, in all three common formats, and then shows you the most useful sum in sports betting: turning odds into an implied chance and spotting the margin. You don't need any math beyond division.
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The three formats
Same price, three ways
| Decimal | Fractional | American | Return on 10 |
|---|---|---|---|
| 1.50 | 1/2 | -200 | 15 |
| 2.00 | 1/1 | +100 | 20 |
| 3.00 | 2/1 | +200 | 30 |
Decimal
Decimal odds are the total you get back for each unit staked, including your stake. A 10 stake at 2.50 returns 25: your 10 back plus 15 profit. To find the profit, subtract 1 from the odds and multiply by your stake. Decimal is the simplest format for math, which is why we use it in our examples.
Fractional
Fractional odds show profit compared with stake. 5/2 means you win 5 for every 2 staked, and you also get your stake back. A 10 stake at 5/2 makes 25 profit and returns 35. Odds of 1/2, called "two to one on", mean you win 1 for every 2 staked, so the selection is the favorite. Fractional odds are traditional in horse racing.
American
American odds, also called moneyline odds, use 100 as the reference. A plus number shows the profit on a 100 stake: plus 250 wins 250. A minus number shows how much you must stake to win 100: minus 200 means staking 200 to win 100. Plus is the underdog, minus is the favorite. They're standard for US sports such as the NFL.
Converting between formats
Conversion rules
| From | To decimal |
|---|---|
| Fractional a/b | a divided by b, plus 1 |
| American plus | The number divided by 100, plus 1 |
| American minus | 100 divided by the number, plus 1 |
Two quick checks: 3/1 is 4.00 in decimal. Minus 150 is 100 divided by 150, which is 0.667, plus 1, so about 1.67. Going back the other way, decimal 1.80 is 4/5 as a fraction and minus 125 in American.
Implied probability
Divide 1 by the decimal odds. 2.00 means 50%. Add up the implied probabilities on all outcomes and you'll get more than 100%. The extra is the bookmaker's margin.
Implied probability is the chance the price suggests. Odds of 4.00 imply 25%. Odds of 1.25 imply 80%. It's the bookmaker's view plus the margin, not the true chance. Nobody knows the true chance for certain.
Spotting the margin
Take a made-up football match priced at 2.40 home, 3.30 draw and 3.00 away. The implied chances are about 41.7%, 30.3% and 33.3%. Together they add up to about 105.3%. That extra 5.3% is the overround, the bookmaker's built-in edge on that market. Two-way markets work the same way: 1.91 on both sides adds up to about 104.7%.
The margin is why betting at random loses money over time. It's also why multiples cost more: each leg in an accumulator carries its own margin, and they multiply. Props and niche markets usually carry bigger margins than the main markets.
What "value" means, and doesn't
People talk about "value" when they think the real chance of an outcome is higher than the implied probability. That idea is correct in principle. In practice, your estimate of the real chance is just an opinion, and the price is the market's opinion with a margin added. Long odds aren't better value because they pay more. Short odds aren't safer because they win more often. Our smarter betting guide covers why records matter more than gut feeling here.
Odds and payouts on Stake
Stake offers a choice of odds formats in its settings. Your bet slip shows the potential return before you confirm. Check that number every time. It's the clearest way to make sure you've entered the stake you meant. Prices can change while a bet is being placed, especially in live betting, and you may be asked to accept a new price.
A worked example
You stake 20 on a team at 2.75. Your potential return is 55, made of 20 stake and 35 profit. In fractional that's 7/4, and in American plus 175. The implied chance is 1 divided by 2.75, about 36.4%. If you think the team wins more often than one time in three, the price suits your view. If not, it doesn't. Either way, it's still a bet you can lose.
Related
Now you can read how to place a bet and accumulators. Handicap and totals lines use the same prices, so handicap betting is a good next step.
Keeping it in proportion
Understanding odds helps you see what a bet costs. It doesn't make betting profitable. The house edge applies to every market. Treat every bet as money you can lose, and if you're chasing losses, stop and read our responsible gambling page.
FAQ
Which format should I use?
Whichever you find easiest. Decimal is the simplest math.
Can I change format on Stake?
Yes, in settings.
Are bigger odds better value?
Not by themselves. Value depends on the real chance.
Why do the implied chances add up to more than 100%?
Because of the bookmaker's margin. The extra is the book's built-in edge on that market.