Every sport, every league, every bookmaker prices its markets slightly differently — but under the surface they all say the same thing. Once you know how to translate the language of odds you can compare any price to any other in seconds.
The three formats you will actually see
There are three dominant formats worldwide. All bookmakers let you switch in the app settings, so learning even one is enough at first.
- Decimal — Europe, Australia, Canada. Example:
2.10 - American — United States. Example:
+110 - Fractional — United Kingdom, Ireland. Example:
11/10
All three of the numbers above describe exactly the same bet.
Decimal odds — the friendly one
Decimal odds are the easiest for math. Your total payout (including stake) is:
Payout = Stake × Odds
A €50 wager at 2.10 pays €105 back if it wins — €55 in profit plus your €50 stake. Anything above 2.00 is an underdog; below 2.00 is a favorite.
American odds — plus and minus
American odds are quoted around a base of $100.
- Negative (−) means "how much you must risk to win $100." −150 means you must stake $150 to win $100.
- Positive (+) means "how much you win from a $100 stake." +150 means a $100 wager pays $150 profit.
Fractional odds — the classic
Fractional odds show profit-to-stake. 5/1 means you win 5 for every 1 you stake, plus your stake back. 4/6 (a favorite) means for every 6 you stake, you win 4 in profit.
The single most useful math trick: implied probability
Every set of odds hides a probability. Once you see it, you can no longer un-see it.
Implied probability = 1 ÷ decimal odds
So 1.50 implies 66.7%. 3.00 implies 33.3%. If your own view is that a bet is 45% likely and the odds imply 33%, you have found value — a bet with positive expected return over the long run.
Conversion cheat sheet
Save this table on your phone. It covers 95% of real-world situations.
| Decimal | American | Fractional | Implied % |
|---|---|---|---|
| 1.50 | −200 | 1/2 | 66.7% |
| 1.80 | −125 | 4/5 | 55.6% |
| 2.00 | +100 | 1/1 (evens) | 50.0% |
| 2.50 | +150 | 3/2 | 40.0% |
| 3.00 | +200 | 2/1 | 33.3% |
| 5.00 | +400 | 4/1 | 20.0% |
The bookmaker's margin (the "overround")
Add the implied probabilities of every outcome in a single market. If the total is greater than 100%, the surplus is the book's built-in margin. On a two-way market (like tennis) a fair market would sum to exactly 100%. A typical online book prices around 104–106%. The best of the best sit at 102%.
Live odds versus opening odds
Prices change constantly. Sharp bettors care about the price at kickoff — the "closing line." Consistently getting a better price than the closing line is the strongest evidence of long-term skill.
Common myths to unlearn
- "Longer odds mean bigger wins." They also mean lower probability of winning. Long-shot lottos are almost always the worst-value markets in a book.
- "Round-number odds are more likely." Books simply round to keep prices readable. There's no probability signal in the digits.
- "Odds are the true probability." They include margin — always adjust before comparing to your own estimate.
Comfortable with the math now? Level up with our full 2026 betting strategy guide.
