How betting odds work
Written by BettingSeeker Editorial Team
What odds tell you
Every price a bookmaker offers does two jobs. It tells you how much you will be paid if you win, and it shows how likely the bookmaker thinks that outcome is. Once you can read both, you can compare bookmakers and spot bets that are better value.
The three formats
The same price can be written three ways. Use our odds converter to switch between them.
| Format | Example | What it means | Where it is used |
|---|---|---|---|
| Fractional | 5/2 | Win 5 for every 2 staked, plus your stake back | UK, Ireland, horse racing |
| Decimal | 3.50 | Total return per 1 staked, stake included | Europe, Australia, Canada, exchanges |
| American | +250 | Profit on a 100 stake | United States |
| American | −200 | Stake needed to win 100 | United States |
Working out your returns
Decimal odds make the maths simplest: returns = stake × decimal odds.
A 10 stake at 3.50 returns 35: that is 25 profit plus your 10 stake. With fractional odds, profit = stake × numerator ÷ denominator, so 10 at 5/2 wins 25 profit, the same result.
Odds and probability
To turn decimal odds into the chance they imply, divide 1 by the odds:
- 2.00 → 1 ÷ 2.00 = 50%
- 3.50 → 1 ÷ 3.50 = 28.6%
- 11.00 → 1 ÷ 11.00 = 9.1%
This is the implied probability. If you believe an outcome is more likely than its implied probability, the bet is good value. If you think it is less likely, it is not.
The bookmaker margin
Add up the implied probabilities of every outcome in a market and the total comes to more than 100%. For a football match priced at 2.10, 3.40 and 3.60, the total is about 104.8%. The extra 4.8% is the margin, also called the overround or vig. It is how bookmakers make money whatever the result.
Margins vary a lot between bookmakers and markets. Lower margins mean better odds for you over time. Check any market with our margin calculator.
Combining odds
When you put several selections into one parlay or accumulator, the decimal odds multiply. Three selections at 2.00, 1.50 and 3.00 give total odds of 9.00. The returns grow quickly, but so does the chance that one selection lets you down, and the margin compounds on every leg. Try it with the parlay calculator.
Frequently asked questions
Do higher odds mean a better bet?
No. Higher odds pay more because the outcome is less likely. A bet is good value only when the real chance of winning is higher than the chance the odds imply.
What does "evens" mean?
Evens is 1/1 in fractional odds, 2.00 in decimal and +100 in American. You win the same amount you staked.
What does odds-on mean?
Odds-on means the bookmaker rates the outcome as more likely than not, such as 1/2 or 1.50. You win less than you stake.