Betting odds show how likely a bookmaker thinks something is to happen, and what you'd get back for each unit you stake. They come in three formats: fractional (common in the UK), decimal (common in Europe and Australia) and American moneyline (used in the US). All three say the same thing in different clothes.
Pick one format, learn it well, and use the table further down to translate the other two. I'll use plain units for every example, so the maths stays about the idea and not about any currency. The numbers are illustrative, not real prices from any bookmaker.
Fractional odds, the UK style
Fractional odds look like 5/1 and are said as 'five to one'. The first number is what you win, and the second is what you stake. So 5/1 means you win 5 units for every 1 unit you put down, and you get your stake back as well.
A worked example
Stake 2 units at 5/1. You win 10 units, and you get your 2 units back, so the total returned is 12 units. If the bet loses, you lose the 2 units. With 1/2, said 'one to two' or 'two to one on', you win 1 unit for every 2 staked. Stake 4 units and you'd win 2 units, with 6 units returned in all. Odds of 1/1 are called evens: you win what you stake.
Decimal odds, the European style
Decimal odds show your total return for each unit staked, stake included. That makes them the easiest format to work with. The bigger the number, the bigger the return, and the less likely the bookmaker thinks the result is.
A worked example
Stake 10 units at 3.00. The total return is 10 multiplied by 3, which is 30 units. Take away your 10-unit stake and your winnings are 20 units. At 1.50, the same 10 units would return 15, so 5 units of winnings. Anything at 2.00 is evens.
American moneyline odds
US odds use a plus or minus sign next to a number, and the number is always measured against 100 units. A minus sign shows how much you'd need to stake to win 100 units. A plus sign shows how much you'd win from a 100-unit stake.
A worked example
At -200, you'd stake 200 units to win 100. At +200, a stake of 100 units wins 200. At +100, you win what you stake, which is evens. Minus numbers always mean the favourite, and plus numbers mean the underdog, which brings us to the next point.
One last tip on reading odds: always check which format a site is showing. Most bookmakers let you switch between fractional, decimal and moneyline in the settings, so you can use whichever you find easiest.
Favourite vs underdog
The favourite is the outcome the bookmaker thinks is most likely, so it has the shorter odds: a small fraction, a low decimal, or a minus moneyline. The underdog has longer odds, and a bigger return if it comes in. Neither is a better bet by default. Short odds pay less because the result is expected more often.
Odds are not a prediction of what will happen. They reflect the bookmaker's view, the bookmaker's margin, and how other people are betting. A favourite loses regularly, and an underdog wins regularly. That's why the odds are what they are.
Turning odds into a chance
Odds hide a chance, called the implied probability. For fractional odds written a/b, the chance is b out of a + b. So 1/1 is about 1 in 2, 2/1 is about 1 in 3, and 5/1 is about 1 in 6. For decimal odds, divide 1 by the number, so 3.00 gives one third.
Remember that this is the chance the odds imply, not the true chance. If you think the real chance is higher than the odds suggest, that's the only situation where a price could look like good value, and even then you can be wrong.
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| Fractional | Decimal | American moneyline | Implied chance |
|---|---|---|---|
| 1/1 (evens) | 2.00 | +100 | about 1 in 2 |
| 2/1 | 3.00 | +200 | about 1 in 3 |
| 1/2 | 1.50 | -200 | about 2 in 3 |
| 5/1 | 6.00 | +500 | about 1 in 6 |
Why the book adds up to more than one
Take every possible outcome of an event, turn each set of odds into its implied chance, and add them up. In a fair world they'd total exactly one whole. At a bookmaker they come to more than one. The extra is the bookmaker's margin, sometimes called the overround, vig or juice.
A simple example is a coin toss. If both sides are offered at 10/11, each side implies slightly more than 1 in 2. Add the two together and you're over one whole. That gap is how the bookmaker expects to come out ahead over many bets, whoever wins any single one. It's also why comparing odds between licensed bookmakers matters: a smaller margin means a better deal for you.
Betting safely
Understanding odds doesn't give you an edge. The odds are set so the bookmaker comes out ahead over time, so treat any bet as paying for entertainment. If you're new, things to know before you gamble online is a sensible read before you start.
- Bet only if you're an adult and betting is legal where you live.
- Set a limit on time and stake before you start, and stick to it.
- Never chase losses, and never bet with money you need for bills.
- Take breaks, and walk away if it stops being fun.
- Don't treat betting as a way to make money.
Free, confidential help is available. In the UK, contact GamCare or BeGambleAware. In the US, the National Council on Problem Gambling runs a helpline and chat service. If gambling is causing you stress, please reach out to one of them.
Want to write about betting yourself?
If you run a gambling business and want to share what you know, here's how to write for my gambling section. Casino brands can find the details on how to write for my casino section.
This is general information, not advice. Gambling is for adults only where it's legal, it should never be a way to make money, and free help is available if it stops being fun.
Frequently asked questions
What does 5/1 mean in betting?
It means you win 5 units for every 1 unit you stake, and your stake comes back too. A 2-unit stake at 5/1 returns 12 units in total: 10 in winnings plus your 2 back.
What do the plus and minus signs mean in American odds?
A minus number is how much you'd need to stake to win 100 units, and it marks the favourite. A plus number is how much you'd win from a 100-unit stake, and it marks the underdog.
Do shorter odds mean a better bet?
No. Shorter odds mean the bookmaker thinks the outcome is more likely, so it pays less. Longer odds pay more because the outcome is expected less often. Neither is better by default.
Can odds tell me who will win?
No. Odds reflect the bookmaker's view, a built-in margin and how people are betting. They show a chance, not a certainty, and favourites lose often.
