Betting odds tell you two things at once: how likely a bookmaker thinks an outcome is, and how much you win if you are right. There are three formats used globally (decimal, fractional, and American), and while they look different, they all say the same thing. This guide breaks each one down with clear examples.
Table of Contents
- Betting odds serve two purposes at once: they reflect the probability of an outcome and they determine your payout if you win.
- There are three main odds formats: decimal, fractional, and American (moneyline). They all express the same information differently.
- Decimal odds are the easiest format for beginners: just multiply your stake by the number to get your total return.
- The higher the odds, the less likely the bookmaker thinks the outcome is, and the bigger the potential payout.
- Bookmakers build a margin (called the “vig” or “overround”) into their odds, meaning the odds are always slightly below true probability.
- Understanding odds is the foundation of all betting decisions. Acting on predictions without understanding odds means betting blind
What Odds Actually Represent
Odds are not invented arbitrarily. Bookmakers analyse statistical data including team form, head-to-head records, injuries, and home advantage to assign each outcome a probability. That probability is then converted into odds.
If a bookmaker believes a team has a 50% chance of winning, the “fair” odds would be 2.00 in decimal format (you double your money). In practice, odds are always set slightly below fair value, because bookmakers build in a profit margin known as the vig, juice, or overround. This is how bookmakers stay profitable over time regardless of individual results.
The Three Formats of Betting Odds
The same odds can be displayed in three different ways depending on where you are betting and which format you prefer. Most modern betting sites allow you to switch between formats in your account settings.
Decimal Odds
Decimal odds are the standard format across Europe, Australia, and on betting exchanges worldwide. They are the most beginner-friendly format because they show your total return (stake included) from a single multiplication.
The formula is simple:
| Decimal Odds | EUR 10 Stake: Total Return | EUR 10 Stake: Profit |
|---|---|---|
| 1.50 | EUR 15.00 | EUR 5.00 |
| 2.00 | EUR 20.00 | EUR 10.00 |
| 3.50 | EUR 35.00 | EUR 25.00 |
| 6.00 | EUR 60.00 | EUR 50.00 |
| 10.00 | EUR 100.00 | EUR 90.00 |
Fractional Odds
Fractional odds are the traditional UK and Irish format, commonly seen in horse racing and on British bookmakers. They express your profit relative to your stake: the left number is what you win, the right number is what you stake.
- Odds of 5/1 (read as “five-to-one”): stake GBP 1, win GBP 5 profit, receive GBP 6 total.
- Odds of 1/2 (read as “one-to-two”): stake GBP 2, win GBP 1 profit, receive GBP 3 total.
| Fractional Odds | Decimal Equivalent | GBP 10 Stake: Profit | GBP 10 Stake: Total Return |
|---|---|---|---|
| 1/2 | 1.50 | GBP 5.00 | GBP 15.00 |
| 1/1 (Evens) | 2.00 | GBP 10.00 | GBP 20.00 |
| 5/2 | 3.50 | GBP 25.00 | GBP 35.00 |
| 5/1 | 6.00 | GBP 50.00 | GBP 60.00 |
| 9/1 | 10.00 | GBP 90.00 | GBP 100.00 |
American (Moneyline) Odds
American odds are the standard format used by sportsbooks in the United States. They use a plus (+) or minus (-) sign to instantly identify underdogs and favourites, with all calculations based around a $100 reference point.
Positive odds (+) are shown for underdogs and show how much profit you make on a $100 bet:
- +200 means: bet $100, win $200 profit, receive $300 total.
Negative odds (-) are shown for favourites and show how much you must bet to win $100 profit:
- -150 means: bet $150, win $100 profit, receive $250 total.
| American Odds | What It Means | $100 Bet: Profit | $100 Bet: Total Return |
|---|---|---|---|
| +500 | Big underdog | $500 | $600 |
| +200 | Underdog | $200 | $300 |
| -120 | Slight favourite | $83.33 | $183.33 |
| -200 | Strong favourite | $50 | $150 |
| -400 | Heavy favourite | $25 | $125 |
How Odds Reflect Probability
Every set of odds has an implied probability: the percentage chance the bookmaker assigns to that outcome happening. Converting odds to probability is one of the most useful skills a bettor can develop, because it lets you assess whether a price represents genuine value.
For example, decimal odds of 2.50 imply a 40% chance of winning (1 / 2.50 = 0.40). If your own analysis suggests the true probability is higher (say 50%), that represents a value bet.
The Bookmaker’s Margin
If you add up the implied probabilities of all outcomes in a match, the total will always exceed 100%. This excess, typically between 3% and 10% depending on the bookmaker and market, is the overround and represents the bookmaker’s built-in profit margin.
Take a simple coin flip offered by a bookmaker at 1.90 on both heads and tails (rather than the “fair” 2.00). The implied probability of each side is 52.6% (1 / 1.90), totalling 105.2%. That extra 5.2% is the bookmaker’s edge on every flip.
Sharp bettors and good prediction services focus on finding odds where the bookmaker’s implied probability is lower than the true probability of the event. That gap is where long-term profit is found.
Why the Odds Format Matters Less Than You Think
Whether your preferred site displays 2.50, 6/4, or +150, those three expressions describe the exact same bet. The format is purely cosmetic: what matters is the underlying probability and payout, not the notation used to display it.
Most bettors settle into one format and become fluent in it. Decimal is recommended for beginners because the number already tells you your total return multiple. Odds converter tools are freely available online for any quick conversion you need.
Odds at a Glance: Quick Reference Table
| If You See | Format | Favourite or Underdog? |
|---|---|---|
| 1.10 to 1.99 | Decimal | Favourite |
| 2.00 | Decimal | Evens (50/50) |
| 2.01 and above | Decimal | Underdog |
| 1/4, 1/2, 4/6 | Fractional | Favourite (odds-on) |
| 1/1 | Fractional | Evens |
| 5/4, 2/1, 10/1 | Fractional | Underdog (odds-against) |
| -200, -150 | American | Favourite |
| +100 | American | Evens |
| +150, +300 | American | Underdog |
FAQ
QWhat are betting odds in simple terms?
QWhich odds format is easiest for beginners?
QDo all betting sites use the same odds format?
QWhy are bookmaker odds not a true reflection of probability?
QWhat does it mean when odds change before a match?
QWhat are value odds?
